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Papers by Peter Reinhardt

Theoretical Chemistry Accounts

Introduction to the honorary volume dedicated to the memory of János G. Ángyán, died too early, o... more Introduction to the honorary volume dedicated to the memory of János G. Ángyán, died too early, on January 22, 2017, at the age of 60. We recall some stations of his life and essential elements of his research.

Theoretical Chemistry Accounts

Physical Review B

An array of point multipoles is used to mimic the long-range Coulomb interactions in a TiO 5 6Ϫ c... more An array of point multipoles is used to mimic the long-range Coulomb interactions in a TiO 5 6Ϫ cluster model designed to describe the adsorption of CO on a rutile surface. The multipoles are derived from the electron density and the concomitant electrostatic potential of a slab model of the ͑110͒ surface of rutile as calculated in a periodic Hartree-Fock approach. The motivation for the use of a cluster model is the possibility of inclusion of electron correlation by means of quantum-chemical methods, which is to date not easily possible in periodic Hartree-Fock calculations. In contrast to an array of point charges based on a Mulliken population analysis of the periodic charge distribution, the distributed multipoles show good agreement of adsorption properties as compared to a slab calculation. Surface relaxation has a significant influence on the binding of the adsorbate. ͓S0163-1829͑96͒08844-3͔

Computational and Theoretical Chemistry

Internuclear forces in a molecule, as an integral over a geometrical factor and the electron dens... more Internuclear forces in a molecule, as an integral over a geometrical factor and the electron density, can be decomposed into a part having as origin promolecular densities of the participating atoms, and a contribution from the deformation density. At the hand of homo-nuclear diatomic molecules we show that the binding energy is linked to the deformation force except for transition metal dimers. However, vibrational frequencies involving pure bond-length variations are rather well reproduced, even for heteroatomic diatomics. For larger assemblies, frequencies for bending modes are underestimated, but the model may serve for a rough analysis of a vibrational spectrum.

Molecular Physics, 2016

At the hand of the adsorption of the metal atoms Zn, Cd and Hg on a graphene sheet we propose a c... more At the hand of the adsorption of the metal atoms Zn, Cd and Hg on a graphene sheet we propose a combination of range-separated hybrid density-functional theory in combination with the incremental scheme in localized orbitals and extrapolation procedures for the description of this type of extended systems. Using only dispersion terms for the long-range part, we were able to obtain results comparable to incremental CCSD(T) calculations. Repulsive three-center increments reduce the overall correlation contribution to the binding energy by 20 %.

STEM CELLS, 2016

Despite decades of research on amyotrophic lateral sclerosis (ALS), there is only one approved dr... more Despite decades of research on amyotrophic lateral sclerosis (ALS), there is only one approved drug, which minimally extends patient survival. Here, we investigated pathophysiological mechanisms underlying ALS using motor neurons (MNs) differentiated from induced pluripotent stem cells (iPSCs) derived from ALS patients carrying mutations in FUS or SOD1. Patient-derived MNs were less active and excitable compared to healthy controls, due to reduced Na 1 /K 1 ratios in both ALS groups accompanied by elevated potassium channel (FUS) and attenuated sodium channel expression levels (FUS, SOD1). ALS iPSC-derived MNs showed elevated endoplasmic reticulum stress (ER) levels and increased caspase activation. Treatment with the FDA approved drug 4-Aminopyridine (4AP) restored ion-channel imbalances, increased neuronal activity levels and decreased ER stress and caspase activation. This study provides novel pathophysiological data, including a mechanistic explanation for the observed hypoexcitability in patient-derived MNs and a new therapeutic strategy to provide neuroprotection in MNs affected by ALS. STEM CELLS 2016;34:1563-1575 SIGNIFICANCE STATEMENT Our primary objective was to characterize the neurophysiology of iPSC-based models of amyotrophic lateral sclerosis (ALS) and, based on these results, to prevent neurodegeneration using targeted pharmacological intervention. We observed that mutant FUS and SOD1 iPSC-derived motor neurons displayed hypoexcitability, which recently has been shown to be a promising target to increase resilience against ALS-associated neurodegeneration. We identified the molecular mechanisms causing this phenotype, which enabled us to define a new therapeutic strategy using the FDA-approved drug 4-Aminopyridine. 4-Aminopyridine is a potassium channel blocker that raised motor neuronal activity and decreased endoplasmic reticulum stress and caspase activation. Our results provide novel pathophysiological data and an innovative treatment concept for symptomatic and neuroprotective therapy in ALS that stands in contrast to current strategies.

Multi-scale Quantum Models for Biocatalysis, 2009

We present an overview of the energy functions used in two Anisotropic Polarizable Molecular Mech... more We present an overview of the energy functions used in two Anisotropic Polarizable Molecular Mechanics (APMM) procedures namely SIBFA (Sum of Interactions Between Fragments Ab initio computed) and GEM (Gaussian Electrostatic Model). As SIBFA is a second generation APMM scheme based on distributed multipoles, GEM is the first third generation APMM as it uses distributed hermite densities obtained from density fitting. The two approaches are formulated and calibrated on the basis of quantum chemistry. They embody nonclassical effects such as electrostatic penetration, exchange-polarization, and charge transfer. We address here the technical issues of anisotropy, nonadditivity, transferability and computational speedup of methods. In addition, we review the several ab initio intermolecular energy decomposition techniques that can be used to refine polarisable force fields. As we summarize their differences and similarities, we present our own scheme based on Fragment Localized Kohn-Sham orbitals through a Singles-Configuration Interaction (CI) procedure. We also present a chemically intuitive method based on the Electron Localization Function (ELF) which allows to unravel the local electrostatic properties beyond atomic centers: i.e., on bonds, lone pairs and π system, an useful asset to understand bonding in molecules in order to build models

Journal of Molecular Structure: THEOCHEM, 2004

We try to decompose the interaction energy of the hydrogen bonded dimer systems HOH⋯NH3, H2O⋯HNH2... more We try to decompose the interaction energy of the hydrogen bonded dimer systems HOH⋯NH3, H2O⋯HNH2, and H2O⋯HNH3+ into several well-defined quantities, using the fragment-based density-functional calculations, Symmetry-adapted perturbation theory, and as well the Heitler–London approach to interaction energies. The theoretical considerations and the numerical results show that despite the different nature of the decomposition schemes common terms beyond the electrostatic

Physical review. B, Condensed matter, Jan 15, 1994

ABSTRACT The periodic Hartree-Fock approach is used in all-electron calculations on bulk rutile (... more ABSTRACT The periodic Hartree-Fock approach is used in all-electron calculations on bulk rutile (TiO2) and various slabs modeling the (001), (100), and (110) surface to study possible geometric and electronic surface relaxations, convergence of properties with slab thickness, and the relative stability of the different surfaces. Results are discussed by means of a Mulliken population analysis, band structures, and the density of states. We find displacements of surface atoms ranging from 5 to nearly 40 pm; the (001) surface appears to be significantly unstable with respect to the other two [(100) and (110)], in accord with experimental findings. Specific features of the density of states projected onto different Ti sites and the relative stability of the different surfaces agree with a possible dissociation behavior of the rutile structure into TiO2 chains, which are calculated to be stable.

ACS Symposium Series, 2012

When using Hartree-Fock (HF) trial wave functions in quantum Monte Carlo calculations, one faces,... more When using Hartree-Fock (HF) trial wave functions in quantum Monte Carlo calculations, one faces, in case of HF instabilities, the HF symmetry dilemma in choosing between the symmetryadapted solution of higher HF energy and symmetry-broken solutions of lower HF energies. In this work, we have examined the HF symmetry dilemma in hydrogen rings which present singlet instabilities for sufficiently large rings. We have found that the symmetry-adapted HF wave function gives a lower energy both in variational Monte Carlo and in fixed-node diffusion Monte Carlo. This indicates that the symmetry-adapted wave function has more accurate nodes than the symmetry-broken wave functions, and thus suggests that spatial symmetry is an important criterion for selecting good trial wave functions.

When using Hartree-Fock (HF) trial wave functions in quantum Monte Carlo calculations, one faces,... more When using Hartree-Fock (HF) trial wave functions in quantum Monte Carlo calculations, one faces, in case of HF instabilities, the HF symmetry dilemma in choosing between the symmetryadapted solution of higher HF energy and symmetry-broken solutions of lower HF energies. In this work, we have examined the HF symmetry dilemma in hydrogen rings which present singlet instabilities for sufficiently large rings. We have found that the symmetry-adapted HF wave function gives a lower energy both in variational Monte Carlo and in fixed-node diffusion Monte Carlo. This indicates that the symmetry-adapted wave function has more accurate nodes than the symmetry-broken wave functions, and thus suggests that spatial symmetry is an important criterion for selecting good trial wave functions.

Physical Review B, 1999

CuF 2 is known to be an antiferromagnetic compound with a weak ferromagnetism due to the anisotro... more CuF 2 is known to be an antiferromagnetic compound with a weak ferromagnetism due to the anisotropy of its monoclinic unit cell ͑Dzialoshinsky-Moriya mechanism͒. We investigate the magnetic ordering of this compound by means of ab initio periodic unrestricted Hartree-Fock calculations and by cluster calculations which employ state-of-the-art configuration interaction expansions and modern density functional theory techniques. The combined use of periodic and cluster models permits us to firmly establish that the antiferromagnetic order arises from the coupling of one-dimensional subunits which themselves exhibit a very small ferromagnetic coupling between Cu neighbor cations. This magnetic order could be anticipated from the close correspondence between CuF 2 and rutile crystal structures. ͓S0163-1829͑99͒15301-3͔

Physical Review B, 1999

CuF 2 is known to be an antiferromagnetic compound with a weak ferromagnetism due to the anisotro... more CuF 2 is known to be an antiferromagnetic compound with a weak ferromagnetism due to the anisotropy of its monoclinic unit cell ͑Dzialoshinsky-Moriya mechanism͒. We investigate the magnetic ordering of this compound by means of ab initio periodic unrestricted Hartree-Fock calculations and by cluster calculations which employ state-of-the-art configuration interaction expansions and modern density functional theory techniques. The combined use of periodic and cluster models permits us to firmly establish that the antiferromagnetic order arises from the coupling of one-dimensional subunits which themselves exhibit a very small ferromagnetic coupling between Cu neighbor cations. This magnetic order could be anticipated from the close correspondence between CuF 2 and rutile crystal structures. ͓S0163-1829͑99͒15301-3͔

Theoretical Chemistry Accounts, 2006

ABSTRACT The dressed diagonal approximation to the self-consistent – size consistent CI, correcte... more ABSTRACT The dressed diagonal approximation to the self-consistent – size consistent CI, corrected for off-diagonal Fock matrix elements in localized orbitals is developed and applied to the ammoniac dimer system. A quite correct correlation energy can be obtained for this system, with a significantly reduced dependence of the results on the choice of the localization procedure. When calculating an interaction energy, the choice of the monomer orbitals and the application of the Boys–Bernardi counterpoise procedure shows in this case an unusual behavior: the correlation energy does not increase with the size of the atomic basis sets. Nevertheless a reasonable potential curve can be obtained.

Theoretical Chemistry Accounts: Theory, Computation, and Modeling (Theoretica Chimica Acta), 1998

A size-consistent ab initio formalism to calculate correlation corrections to ionization potentia... more A size-consistent ab initio formalism to calculate correlation corrections to ionization potentials as well as electron anities of periodic systems is presented. Our approach is based on a Hartree-Fock scheme which directly yields local orbitals without any a posteriori localization step. The use of local orbitals implies nonzero o-diagonal matrix elements of the Fock operator, which are treated as an additional perturbation and give rise to localization diagrams. Based on the obtained local orbitals, an eective Bloch Hamiltonian is constructed to second order of perturbation theory with all third-order localization diagrams included. In addition, the summation of certain classes of diagrams up to in®nite order in the o-diagonal Fock elements as well as the Epstein-Nesbet partitioning of the full Hamiltonian are discussed. The problem of intruder states, frequently encountered in many-body perturbation theory, is dealt with by employing the theory of intermediate Hamiltonians. As model systems we have chosen cyclic periodic structures up to an oligoethylene ring in double-zeta basis; however, the theory presented here straightforwardly carries over to in®nite periodic systems.

Theoretical Chemistry Accounts: Theory, Computation, and Modeling (Theoretica Chimica Acta), 2000

The techniques of matrix dressing for con®guration-interaction (CI)-type or coupled-electron-pair... more The techniques of matrix dressing for con®guration-interaction (CI)-type or coupled-electron-pairapproximation (CEPA)-type correlation treatments are reviewed with respect to the application to periodic systems. All methods ranging from canonical secondorder Mller±Plesset perturbation theory over CI of single and double excitation, CEPA-0 or the averagedcoupled-pair-functional to self-consistent size-consistent CI can be formulated completely equivalently as an eigenvalue problem or as a solution to a system of linear equations. The size consistency of each method is obtained in a natural way, and invariance under orbital rotations is clearly assessible. A remark on the size consistency of the Davidson correction is presented. Additionally, the direct generation of localized Hartree± Fock orbitals as basic ingredients for the correlation calculations are addressed, as well as selected results on ring molecules, polymers, and 3D cubic beryllium as a model crystal.

Surface Science, 2000

ABSTRACT The geometrical structure of the polar, Al-terminated surface of corundum has been inves... more ABSTRACT The geometrical structure of the polar, Al-terminated surface of corundum has been investigated by different theoretical methods ranging from empirical pair potentials to periodic Hartree–Fock or density functional theory calculations. The different methods agree in predicting a structure for the bulk, which is close to the experimental one, and an inward relaxation of more than 50% in agreement with experiment. However, a rather strong disagreement exists concerning the quantitative amount of relaxation of the surface layers. Accurate density functional theory calculations for slab models considering up to 18 layers with 30 atoms in the unit cell strongly suggest that the degree of relaxation of the outermost Al atomic layer is much larger than the values obtained by other methods. Reasons for the different description are given and implications for the use of pair potentials discussed.

STEM CELLS, 2011

Human adult germline stem cells (haGSCs) were established from human testicular biopsies and were... more Human adult germline stem cells (haGSCs) were established from human testicular biopsies and were claimed to be pluripotent. Recently, the gene expression profile of haGSCs demonstrated that these cells presented with a fibroblast rather than a pluripotent identity. Nevertheless, haGSCs were reported to generate teratomas. In this report, we address this discrepancy. Instead of using haGSCs, which are no longer available for the stem cell community, we used a human testicular fibroblastic cell (hTFC) line that presents with a gene expression profile highly similar to that of haGSCs. Indeed, as shown by microarray analysis, the similarity between hTFCs and haGSCs is comparable to human embryonic stem cell (hESC) lines derived by different laboratories. We argue that the almost identical gene expression profile of hTFCs and haGSCs should result in a very similar if not identical differentiation potential. Strikingly, hTFCs were not able to generate teratomas after injection into nude ...

Journal of Chemical Theory and Computation, 2010

The hydration free energy, structure, and dynamics of the zinc divalent cation are studied using ... more The hydration free energy, structure, and dynamics of the zinc divalent cation are studied using a polarizable force field in molecular dynamics simulations. Parameters for the Zn 2+ are derived from gas-phase ab initio calculation of the Zn 2+-water dimer. The Thole-based dipole polarization is adjusted on the basis of the constrained space orbital variations (CSOV) calculation, while the symmetry adapted perturbation theory (SAPT) approach is also discussed. The vdW parameters of Zn 2+ have been obtained by comparing the AMOEBA Zn 2+-water dimerization energy with results from several theory levels and basis sets over a range of distances. Molecular dynamics simulations of Zn 2+ solvation in bulk water are subsequently performed with the polarizable force field. The calculated first-shell water coordination number, water residence time, and free energy of hydration are consistent with experimental and previous theoretical values. The study is supplemented with extensive reduced variational space (RVS) and electron localization function (ELF) computations in order to unravel the nature of the bonding in Zn 2+ (H 2 O) n (n) 1, 6) complexes and to analyze the charge transfer contribution to the complexes. Results show that the importance of charge transfer decreases as the size of the Zn-water cluster grows due to anticooperativity and to changes in the nature of the metal-ligand bonds. Induction could be dominated by polarization when the system approaches the condensed phase and the covalent effects are eliminated from the Zn(II)-water interaction. To construct an "effective" classical polarizable potential for Zn 2+ in bulk water, one should therefore avoid overfitting to the ab initio charge transfer energy of the Zn 2+-water dimer. Indeed, in order to avoid overestimation of the condensed-phase many-body effects, which is crucial to the transferability of polarizable molecular dynamics, charge transfer should not be included within the classical polarization contribution and should preferably be either incorporated into the pairwise van der Waals contribution or treated explicitly.

Theoretical Chemistry Accounts

Introduction to the honorary volume dedicated to the memory of János G. Ángyán, died too early, o... more Introduction to the honorary volume dedicated to the memory of János G. Ángyán, died too early, on January 22, 2017, at the age of 60. We recall some stations of his life and essential elements of his research.

Theoretical Chemistry Accounts

Physical Review B

An array of point multipoles is used to mimic the long-range Coulomb interactions in a TiO 5 6Ϫ c... more An array of point multipoles is used to mimic the long-range Coulomb interactions in a TiO 5 6Ϫ cluster model designed to describe the adsorption of CO on a rutile surface. The multipoles are derived from the electron density and the concomitant electrostatic potential of a slab model of the ͑110͒ surface of rutile as calculated in a periodic Hartree-Fock approach. The motivation for the use of a cluster model is the possibility of inclusion of electron correlation by means of quantum-chemical methods, which is to date not easily possible in periodic Hartree-Fock calculations. In contrast to an array of point charges based on a Mulliken population analysis of the periodic charge distribution, the distributed multipoles show good agreement of adsorption properties as compared to a slab calculation. Surface relaxation has a significant influence on the binding of the adsorbate. ͓S0163-1829͑96͒08844-3͔

Computational and Theoretical Chemistry

Internuclear forces in a molecule, as an integral over a geometrical factor and the electron dens... more Internuclear forces in a molecule, as an integral over a geometrical factor and the electron density, can be decomposed into a part having as origin promolecular densities of the participating atoms, and a contribution from the deformation density. At the hand of homo-nuclear diatomic molecules we show that the binding energy is linked to the deformation force except for transition metal dimers. However, vibrational frequencies involving pure bond-length variations are rather well reproduced, even for heteroatomic diatomics. For larger assemblies, frequencies for bending modes are underestimated, but the model may serve for a rough analysis of a vibrational spectrum.

Molecular Physics, 2016

At the hand of the adsorption of the metal atoms Zn, Cd and Hg on a graphene sheet we propose a c... more At the hand of the adsorption of the metal atoms Zn, Cd and Hg on a graphene sheet we propose a combination of range-separated hybrid density-functional theory in combination with the incremental scheme in localized orbitals and extrapolation procedures for the description of this type of extended systems. Using only dispersion terms for the long-range part, we were able to obtain results comparable to incremental CCSD(T) calculations. Repulsive three-center increments reduce the overall correlation contribution to the binding energy by 20 %.

STEM CELLS, 2016

Despite decades of research on amyotrophic lateral sclerosis (ALS), there is only one approved dr... more Despite decades of research on amyotrophic lateral sclerosis (ALS), there is only one approved drug, which minimally extends patient survival. Here, we investigated pathophysiological mechanisms underlying ALS using motor neurons (MNs) differentiated from induced pluripotent stem cells (iPSCs) derived from ALS patients carrying mutations in FUS or SOD1. Patient-derived MNs were less active and excitable compared to healthy controls, due to reduced Na 1 /K 1 ratios in both ALS groups accompanied by elevated potassium channel (FUS) and attenuated sodium channel expression levels (FUS, SOD1). ALS iPSC-derived MNs showed elevated endoplasmic reticulum stress (ER) levels and increased caspase activation. Treatment with the FDA approved drug 4-Aminopyridine (4AP) restored ion-channel imbalances, increased neuronal activity levels and decreased ER stress and caspase activation. This study provides novel pathophysiological data, including a mechanistic explanation for the observed hypoexcitability in patient-derived MNs and a new therapeutic strategy to provide neuroprotection in MNs affected by ALS. STEM CELLS 2016;34:1563-1575 SIGNIFICANCE STATEMENT Our primary objective was to characterize the neurophysiology of iPSC-based models of amyotrophic lateral sclerosis (ALS) and, based on these results, to prevent neurodegeneration using targeted pharmacological intervention. We observed that mutant FUS and SOD1 iPSC-derived motor neurons displayed hypoexcitability, which recently has been shown to be a promising target to increase resilience against ALS-associated neurodegeneration. We identified the molecular mechanisms causing this phenotype, which enabled us to define a new therapeutic strategy using the FDA-approved drug 4-Aminopyridine. 4-Aminopyridine is a potassium channel blocker that raised motor neuronal activity and decreased endoplasmic reticulum stress and caspase activation. Our results provide novel pathophysiological data and an innovative treatment concept for symptomatic and neuroprotective therapy in ALS that stands in contrast to current strategies.

Multi-scale Quantum Models for Biocatalysis, 2009

We present an overview of the energy functions used in two Anisotropic Polarizable Molecular Mech... more We present an overview of the energy functions used in two Anisotropic Polarizable Molecular Mechanics (APMM) procedures namely SIBFA (Sum of Interactions Between Fragments Ab initio computed) and GEM (Gaussian Electrostatic Model). As SIBFA is a second generation APMM scheme based on distributed multipoles, GEM is the first third generation APMM as it uses distributed hermite densities obtained from density fitting. The two approaches are formulated and calibrated on the basis of quantum chemistry. They embody nonclassical effects such as electrostatic penetration, exchange-polarization, and charge transfer. We address here the technical issues of anisotropy, nonadditivity, transferability and computational speedup of methods. In addition, we review the several ab initio intermolecular energy decomposition techniques that can be used to refine polarisable force fields. As we summarize their differences and similarities, we present our own scheme based on Fragment Localized Kohn-Sham orbitals through a Singles-Configuration Interaction (CI) procedure. We also present a chemically intuitive method based on the Electron Localization Function (ELF) which allows to unravel the local electrostatic properties beyond atomic centers: i.e., on bonds, lone pairs and π system, an useful asset to understand bonding in molecules in order to build models

Journal of Molecular Structure: THEOCHEM, 2004

We try to decompose the interaction energy of the hydrogen bonded dimer systems HOH⋯NH3, H2O⋯HNH2... more We try to decompose the interaction energy of the hydrogen bonded dimer systems HOH⋯NH3, H2O⋯HNH2, and H2O⋯HNH3+ into several well-defined quantities, using the fragment-based density-functional calculations, Symmetry-adapted perturbation theory, and as well the Heitler–London approach to interaction energies. The theoretical considerations and the numerical results show that despite the different nature of the decomposition schemes common terms beyond the electrostatic

Physical review. B, Condensed matter, Jan 15, 1994

ABSTRACT The periodic Hartree-Fock approach is used in all-electron calculations on bulk rutile (... more ABSTRACT The periodic Hartree-Fock approach is used in all-electron calculations on bulk rutile (TiO2) and various slabs modeling the (001), (100), and (110) surface to study possible geometric and electronic surface relaxations, convergence of properties with slab thickness, and the relative stability of the different surfaces. Results are discussed by means of a Mulliken population analysis, band structures, and the density of states. We find displacements of surface atoms ranging from 5 to nearly 40 pm; the (001) surface appears to be significantly unstable with respect to the other two [(100) and (110)], in accord with experimental findings. Specific features of the density of states projected onto different Ti sites and the relative stability of the different surfaces agree with a possible dissociation behavior of the rutile structure into TiO2 chains, which are calculated to be stable.

ACS Symposium Series, 2012

When using Hartree-Fock (HF) trial wave functions in quantum Monte Carlo calculations, one faces,... more When using Hartree-Fock (HF) trial wave functions in quantum Monte Carlo calculations, one faces, in case of HF instabilities, the HF symmetry dilemma in choosing between the symmetryadapted solution of higher HF energy and symmetry-broken solutions of lower HF energies. In this work, we have examined the HF symmetry dilemma in hydrogen rings which present singlet instabilities for sufficiently large rings. We have found that the symmetry-adapted HF wave function gives a lower energy both in variational Monte Carlo and in fixed-node diffusion Monte Carlo. This indicates that the symmetry-adapted wave function has more accurate nodes than the symmetry-broken wave functions, and thus suggests that spatial symmetry is an important criterion for selecting good trial wave functions.

When using Hartree-Fock (HF) trial wave functions in quantum Monte Carlo calculations, one faces,... more When using Hartree-Fock (HF) trial wave functions in quantum Monte Carlo calculations, one faces, in case of HF instabilities, the HF symmetry dilemma in choosing between the symmetryadapted solution of higher HF energy and symmetry-broken solutions of lower HF energies. In this work, we have examined the HF symmetry dilemma in hydrogen rings which present singlet instabilities for sufficiently large rings. We have found that the symmetry-adapted HF wave function gives a lower energy both in variational Monte Carlo and in fixed-node diffusion Monte Carlo. This indicates that the symmetry-adapted wave function has more accurate nodes than the symmetry-broken wave functions, and thus suggests that spatial symmetry is an important criterion for selecting good trial wave functions.

Physical Review B, 1999

CuF 2 is known to be an antiferromagnetic compound with a weak ferromagnetism due to the anisotro... more CuF 2 is known to be an antiferromagnetic compound with a weak ferromagnetism due to the anisotropy of its monoclinic unit cell ͑Dzialoshinsky-Moriya mechanism͒. We investigate the magnetic ordering of this compound by means of ab initio periodic unrestricted Hartree-Fock calculations and by cluster calculations which employ state-of-the-art configuration interaction expansions and modern density functional theory techniques. The combined use of periodic and cluster models permits us to firmly establish that the antiferromagnetic order arises from the coupling of one-dimensional subunits which themselves exhibit a very small ferromagnetic coupling between Cu neighbor cations. This magnetic order could be anticipated from the close correspondence between CuF 2 and rutile crystal structures. ͓S0163-1829͑99͒15301-3͔

Physical Review B, 1999

CuF 2 is known to be an antiferromagnetic compound with a weak ferromagnetism due to the anisotro... more CuF 2 is known to be an antiferromagnetic compound with a weak ferromagnetism due to the anisotropy of its monoclinic unit cell ͑Dzialoshinsky-Moriya mechanism͒. We investigate the magnetic ordering of this compound by means of ab initio periodic unrestricted Hartree-Fock calculations and by cluster calculations which employ state-of-the-art configuration interaction expansions and modern density functional theory techniques. The combined use of periodic and cluster models permits us to firmly establish that the antiferromagnetic order arises from the coupling of one-dimensional subunits which themselves exhibit a very small ferromagnetic coupling between Cu neighbor cations. This magnetic order could be anticipated from the close correspondence between CuF 2 and rutile crystal structures. ͓S0163-1829͑99͒15301-3͔

Theoretical Chemistry Accounts, 2006

ABSTRACT The dressed diagonal approximation to the self-consistent – size consistent CI, correcte... more ABSTRACT The dressed diagonal approximation to the self-consistent – size consistent CI, corrected for off-diagonal Fock matrix elements in localized orbitals is developed and applied to the ammoniac dimer system. A quite correct correlation energy can be obtained for this system, with a significantly reduced dependence of the results on the choice of the localization procedure. When calculating an interaction energy, the choice of the monomer orbitals and the application of the Boys–Bernardi counterpoise procedure shows in this case an unusual behavior: the correlation energy does not increase with the size of the atomic basis sets. Nevertheless a reasonable potential curve can be obtained.

Theoretical Chemistry Accounts: Theory, Computation, and Modeling (Theoretica Chimica Acta), 1998

A size-consistent ab initio formalism to calculate correlation corrections to ionization potentia... more A size-consistent ab initio formalism to calculate correlation corrections to ionization potentials as well as electron anities of periodic systems is presented. Our approach is based on a Hartree-Fock scheme which directly yields local orbitals without any a posteriori localization step. The use of local orbitals implies nonzero o-diagonal matrix elements of the Fock operator, which are treated as an additional perturbation and give rise to localization diagrams. Based on the obtained local orbitals, an eective Bloch Hamiltonian is constructed to second order of perturbation theory with all third-order localization diagrams included. In addition, the summation of certain classes of diagrams up to in®nite order in the o-diagonal Fock elements as well as the Epstein-Nesbet partitioning of the full Hamiltonian are discussed. The problem of intruder states, frequently encountered in many-body perturbation theory, is dealt with by employing the theory of intermediate Hamiltonians. As model systems we have chosen cyclic periodic structures up to an oligoethylene ring in double-zeta basis; however, the theory presented here straightforwardly carries over to in®nite periodic systems.

Theoretical Chemistry Accounts: Theory, Computation, and Modeling (Theoretica Chimica Acta), 2000

The techniques of matrix dressing for con®guration-interaction (CI)-type or coupled-electron-pair... more The techniques of matrix dressing for con®guration-interaction (CI)-type or coupled-electron-pairapproximation (CEPA)-type correlation treatments are reviewed with respect to the application to periodic systems. All methods ranging from canonical secondorder Mller±Plesset perturbation theory over CI of single and double excitation, CEPA-0 or the averagedcoupled-pair-functional to self-consistent size-consistent CI can be formulated completely equivalently as an eigenvalue problem or as a solution to a system of linear equations. The size consistency of each method is obtained in a natural way, and invariance under orbital rotations is clearly assessible. A remark on the size consistency of the Davidson correction is presented. Additionally, the direct generation of localized Hartree± Fock orbitals as basic ingredients for the correlation calculations are addressed, as well as selected results on ring molecules, polymers, and 3D cubic beryllium as a model crystal.

Surface Science, 2000

ABSTRACT The geometrical structure of the polar, Al-terminated surface of corundum has been inves... more ABSTRACT The geometrical structure of the polar, Al-terminated surface of corundum has been investigated by different theoretical methods ranging from empirical pair potentials to periodic Hartree–Fock or density functional theory calculations. The different methods agree in predicting a structure for the bulk, which is close to the experimental one, and an inward relaxation of more than 50% in agreement with experiment. However, a rather strong disagreement exists concerning the quantitative amount of relaxation of the surface layers. Accurate density functional theory calculations for slab models considering up to 18 layers with 30 atoms in the unit cell strongly suggest that the degree of relaxation of the outermost Al atomic layer is much larger than the values obtained by other methods. Reasons for the different description are given and implications for the use of pair potentials discussed.

STEM CELLS, 2011

Human adult germline stem cells (haGSCs) were established from human testicular biopsies and were... more Human adult germline stem cells (haGSCs) were established from human testicular biopsies and were claimed to be pluripotent. Recently, the gene expression profile of haGSCs demonstrated that these cells presented with a fibroblast rather than a pluripotent identity. Nevertheless, haGSCs were reported to generate teratomas. In this report, we address this discrepancy. Instead of using haGSCs, which are no longer available for the stem cell community, we used a human testicular fibroblastic cell (hTFC) line that presents with a gene expression profile highly similar to that of haGSCs. Indeed, as shown by microarray analysis, the similarity between hTFCs and haGSCs is comparable to human embryonic stem cell (hESC) lines derived by different laboratories. We argue that the almost identical gene expression profile of hTFCs and haGSCs should result in a very similar if not identical differentiation potential. Strikingly, hTFCs were not able to generate teratomas after injection into nude ...

Journal of Chemical Theory and Computation, 2010

The hydration free energy, structure, and dynamics of the zinc divalent cation are studied using ... more The hydration free energy, structure, and dynamics of the zinc divalent cation are studied using a polarizable force field in molecular dynamics simulations. Parameters for the Zn 2+ are derived from gas-phase ab initio calculation of the Zn 2+-water dimer. The Thole-based dipole polarization is adjusted on the basis of the constrained space orbital variations (CSOV) calculation, while the symmetry adapted perturbation theory (SAPT) approach is also discussed. The vdW parameters of Zn 2+ have been obtained by comparing the AMOEBA Zn 2+-water dimerization energy with results from several theory levels and basis sets over a range of distances. Molecular dynamics simulations of Zn 2+ solvation in bulk water are subsequently performed with the polarizable force field. The calculated first-shell water coordination number, water residence time, and free energy of hydration are consistent with experimental and previous theoretical values. The study is supplemented with extensive reduced variational space (RVS) and electron localization function (ELF) computations in order to unravel the nature of the bonding in Zn 2+ (H 2 O) n (n) 1, 6) complexes and to analyze the charge transfer contribution to the complexes. Results show that the importance of charge transfer decreases as the size of the Zn-water cluster grows due to anticooperativity and to changes in the nature of the metal-ligand bonds. Induction could be dominated by polarization when the system approaches the condensed phase and the covalent effects are eliminated from the Zn(II)-water interaction. To construct an "effective" classical polarizable potential for Zn 2+ in bulk water, one should therefore avoid overfitting to the ab initio charge transfer energy of the Zn 2+-water dimer. Indeed, in order to avoid overestimation of the condensed-phase many-body effects, which is crucial to the transferability of polarizable molecular dynamics, charge transfer should not be included within the classical polarization contribution and should preferably be either incorporated into the pairwise van der Waals contribution or treated explicitly.