Per-Åke Malmqvist | Lund University (original) (raw)
Papers by Per-Åke Malmqvist
Numerical Determination of the Electronic Structure of Atoms, Diatomic and Polyatomic Molecules, 1989
Restricted Active Space (RAS) SCF calculations have been performed of the potential curves for th... more Restricted Active Space (RAS) SCF calculations have been performed of the potential curves for the X 3 Z -and A3H states of the OH + ion and on the lifetime of the v = 0 -2 vibrational levels of the A state. The convergence of the transition moment integral as a function of the size of the active orbital space was used to select the active orbitals. The calculated value of the v = 0 lifetime is 2.4 #s. An estimate of the errors remaining in the calculation leads to a final theoretical value of 2.7 __+ 0.1/~s. Computed bond distances and bond energies are 1.031 (1.029)/~ and 5.05 (5.01) eV, respectively, for the X state, and 1.137 (1.135)/~ and 1.57 eV, respectively, for the A state (experimental values within parenthesis).
When a molecular equilibrium geometry is determined by minimizing the energy by a quasi-Newton-Ra... more When a molecular equilibrium geometry is determined by minimizing the energy by a quasi-Newton-Raphson method, the number of iterations required depends critically on the choice of an approximate molecular Hessian matrix. We find that a simple 15-parameter function ...
Chemical Physics Letters, 1996
It has recently been shown that Møller-Plesset perturbation calculations may diverge for single c... more It has recently been shown that Møller-Plesset perturbation calculations may diverge for single configuration dominated systems in extended basis sets. We examine the origin of this divergence using the neon atom as a test example. The lowest energies for total symmetric states are calculated for values of the perturbation parameter strength zϵ[−1, 1]. For z ≈ (−0.9)−(−0.8) avoided crossings between
Journal of The American Chemical Society, 2006
Fundamental World of Quantum Chemistry, 2003
Theoretical Chemistry Accounts: Theory, Computation, and Modeling (Theoretica Chimica Acta), 2004
... Savin [7] and Gra®fenstein and Cremer [8] have formulated theories which combine DFT with a m... more ... Savin [7] and Gra®fenstein and Cremer [8] have formulated theories which combine DFT with a multiconfigurational description of the wave ... Sergey Gusarov, Per-A˚ke Malmqvist, Roland Lindh, Bjo®rn O. Roos Department of Theoretical Chemistry, Chemical Center, POBox 124 ...
Theoretica Chimica Acta, 1990
Generally contracted basis sets for first row atoms have been constructed using the Atomic Natura... more Generally contracted basis sets for first row atoms have been constructed using the Atomic Natural Orbital (ANO) approach, with modifications for allowing symmetry breaking and state averaging. The ANOs are constructed by averaging over several atomic states, positive and negative ions, and atoms in an external electric field. The contracted basis sets give virtually identical results as the corresponding uncontracted sets for the atomic properties, which they have been designed to reproduce. The design objective has been to describe the ionization potential, the electron affinity, and the polarizability as accurately as possible. The result is a set of well-balanced basis sets for molecular calculations.
The Journal of Physical Chemistry A, 2008
New basis sets of the atomic natural orbital (ANO) type have been developed for the lanthanide at... more New basis sets of the atomic natural orbital (ANO) type have been developed for the lanthanide atoms La-Lu. The ANOs have been obtained from the average density matrix of the ground and lowest excited states of the atom, the positive ions, and the atom in an electric field. Scalar relativistic effects are included through the use of a Douglas-Kroll-Hess Hamiltonian. Multiconfigurational wave functions have been used with dynamic correlation included using second-order perturbation theory (CASSCF/CASPT2). The basis sets are applied in calculations of ionization energies and some excitation energies. Computed ionization energies have an accuracy better than 0.1 eV in most cases. Two molecular applications are included as illustration: the cerium diatom and the LuF3 molecule. In both cases it is shown that 4f orbitals are not involved in the chemical bond in contrast to an earlier claim for the latter molecule.
The Journal of Physical Chemistry A, 2005
New basis sets of the atomic natural orbital (ANO) type have been developed for the first, second... more New basis sets of the atomic natural orbital (ANO) type have been developed for the first, second, and third row transition metal atoms. The ANOs have been obtained from the average density matrix of the ground and lowest excited states of the atom, the positive and negative ions, and the atom in an electric field. Scalar relativistic effects are included through the use of a Douglas-Kroll-Hess Hamiltonian. Multiconfigurational wave functions have been used with dynamic correlation included using second order perturbation theory (CASSCF/CASPT2). The basis sets are applied in calculations of ionization energies, electron affinities, and excitation energies for all atoms and polarizabilities for spherically symmetric atoms. These calculations include spin-orbit coupling using a variation-perturbation approach. Computed ionization energies have an accuracy better than 0.2 eV in most cases. The accuracy of computed electron affinities is the same except in cases where the experimental values are smaller than 0.5 eV. Accurate results are obtained for the polarizabilities of atoms with spherical symmetry. Multiplet levels are presented for some of the third row transition metals.
The Journal of Physical Chemistry A, 2001
The structure and vibrational frequencies of the UO 2 molecule have been determined using multico... more The structure and vibrational frequencies of the UO 2 molecule have been determined using multiconfigurational wave functions (CASSCF/CASPT2), together with a newly developed method to treat spin-orbit coupling. The molecule has been found to have a (5fφ)(7s), 3 Φ u , Ω ) 2 ground state with a U-O bond distance of 1.77 Å. The computed antisymmetric stretching σ u frequency is 923 cm -1 with a 16/18 isotope ratio of 1.0525 which compares with the experimental values of 915 cm -1 and 1.0526, respectively. Calculations of the first adiabatic ionization energy gave the value 6.17 eV, which is 0.7 eV larger than the currently accepted experimental result. Reasons for this difference are suggested.
The Journal of Physical Chemistry A, 2004
New basis sets of the atomic natural orbital (ANO) type have been developed for the main group an... more New basis sets of the atomic natural orbital (ANO) type have been developed for the main group and rare gas atoms. The ANO's have been obtained from the average density matrix of the ground and lowest excited states of the atom, the positive and negative ions, and the dimer at its ...
Physical Chemistry Chemical Physics, 2000
Page 1. On the low-lying singlet excited states of styrene: a theoretical contribution¤ Vicent Mo... more Page 1. On the low-lying singlet excited states of styrene: a theoretical contribution¤ Vicent Molina,a Manuela O. Roosb and Malmqvistb Mercha n,a Bjo rn Per-A ke a Departamento de Universitat de Dr. Moliner 50, Burjassot, E-46100 Qu• mica F• sica, V ale`ncia, ...
Molecular Physics, 2004
... Sergey Gusarov, Per-Åke Malmqvist * & Roland Lindh pages 2207-221... more ... Sergey Gusarov, Per-Åke Malmqvist * & Roland Lindh pages 2207-2216. ... Colle, R and Salvetti, O. 1990. J. chem. Phys. , 93: 534 [CrossRef], [Web of Science ®] View all references15]15. Pollet, P, Savin, A, Leininger, T and Stoll, H. 2002. J. chem. Phys. ...
Journal of Chemical Theory and Computation, 2008
The electronic structure and low-lying electronic states of a Co(III)(diiminato)(NPh) complex hav... more The electronic structure and low-lying electronic states of a Co(III)(diiminato)(NPh) complex have been studied using multiconfigurational wave function theory (CASSCF/CASPT2). The results have been compared to those obtained with density functional theory. The best agreement with ab initio results is obtained with a modified B3LYP functional containing a reduced amount (15%) of Hartree-Fock exchange. A relativistic basis set with 869 functions has been employed in the most extensive ab initio calculations, where a Cholesky decomposition technique was used to overcome problems arising from the large size of the two-electron integral matrix. It is shown that this approximation reproduces results obtained with the full integral set to a high accuracy, thus opening the possibility to use this approach to perform multiconfigurational wave-function-based quantum chemistry on much larger systems relative to what has been possible until now.
The Journal of Chemical Physics, 1992
The recently implemented second-order perturbation theory based on a complete active space self-c... more The recently implemented second-order perturbation theory based on a complete active space self-consistent field reference function has been extended by allowing the Fock-type oneelectron operator, which defines the zeroth-order Hamiltonian to have nonzero elements also in nondiagonal matrix blocks. The computer implementation is now less straightforward and more computer time will be needed in obtaining the second-order energy. The method is illustrated in a series of calculations on N 2 , NO, 02' CH 3 , CH 2 , and F-.
The Journal of Chemical Physics, 2009
A general expression for the distribution of the fluctuating 2 ᐉ -pole moment M ᐉ of a spherical ... more A general expression for the distribution of the fluctuating 2 ᐉ -pole moment M ᐉ of a spherical sample of dielectric material is derived on the basis of dielectric theory combined with statistical mechanics. The formulas are compared with results from computer simulations of a weakly coupled Stockmayer fluid and the agreement is shown to be excellent. Furthermore, we calculate the size of the coupling, quantified through the free energy of solvation A solv , of the fluctuating electric moments to a surrounding dielectric medium. It turns out that the contribution to A solv from each fluctuating electric moment actually increases with increasing order ᐉ of the moment, resulting in a formally infinite free energy of solvation. We also present a correction to A solv for molecular media, which shows that the molecular nature of the surrounding medium effectively suppresses the divergence in the solvation free energy.
International Journal of Quantum Chemistry, 2009
Previous studies on photo dissociation of iodobenzene by Bersohn 1, El-Sayed 24, Smalley 5 and L... more Previous studies on photo dissociation of iodobenzene by Bersohn 1, El-Sayed 24, Smalley 5 and Leone 6 revealed two distinct mechanisms: a direct dissociation caused by an excitation to the anti bonding n−σ* state, and a pre dissociative mechanism, where the initial ...
Inorganic Chemistry, 2007
Uranium atoms activate methane upon ultraviolet excitation to form the methyl uranium hydride CH3... more Uranium atoms activate methane upon ultraviolet excitation to form the methyl uranium hydride CH3-UH, which undergoes alpha-H transfer to produce uranium methylidene dihydride, CH2=UH2. This rearrangement most likely occurs on an excited-quintet potential-energy surface and is followed by relaxation in the argon matrix. These simple U+CH4 reaction products are identified through isotopic substitution (13CH4, CD4, CH2D2) and density functional theory frequency and structure calculations for the strong U-H stretching modes. Relativistic multiconfiguration (CASSCF/CASPT2) calculations substantiate the agostic distorted C1 ground-state structure for the triplet CH2=UH2 molecule. We find that uranium atoms are less reactive in methane activation than thorium atoms. Our calculations show that the CH2=UH2 complex is distorted more than CH2=ThH2. A favorable interaction between the low energy open-shell U(5f) sigma orbital and the agostic hydrogen contributes to the distortion in the uranium methylidene complexes.
ChemPhysChem, 2007
The computation of the electronic g tensor by two multireference methods is presented and applied... more The computation of the electronic g tensor by two multireference methods is presented and applied to a selection of molecules including CN, BO, AlO, GaO, InO, ZnH, ZnF, O(2), H(2)O(+), O(3) (-), and H(2)CO(+) (group A) as well as TiF(3), CuCl(4) (2-), Cu(NH(3))(4) (2+), and a series of d(1)-MOX(4) (n-) compounds, with M=V, Cr, Mo, Tc, W, Re and X=F, Cl, Br (group B). Two approaches are considered, namely, one in which spin-orbit coupling and the Zeeman effect are included using second-order perturbation theory and another one in which the Zeeman effect is added through first-order degenerate perturbation theory within the ground-state Kramers doublet. The two methods have been implemented into the MOLCAS quantum chemistry software package. The results obtained for the molecules in group A are in good agreement with experiment and with previously reported calculated g values. The results for the molecules in group B vary. While the g values for the d(1) systems are superior to previous theoretical results, those obtained for the d(9) systems are too large compared to the experimental values.
Numerical Determination of the Electronic Structure of Atoms, Diatomic and Polyatomic Molecules, 1989
Restricted Active Space (RAS) SCF calculations have been performed of the potential curves for th... more Restricted Active Space (RAS) SCF calculations have been performed of the potential curves for the X 3 Z -and A3H states of the OH + ion and on the lifetime of the v = 0 -2 vibrational levels of the A state. The convergence of the transition moment integral as a function of the size of the active orbital space was used to select the active orbitals. The calculated value of the v = 0 lifetime is 2.4 #s. An estimate of the errors remaining in the calculation leads to a final theoretical value of 2.7 __+ 0.1/~s. Computed bond distances and bond energies are 1.031 (1.029)/~ and 5.05 (5.01) eV, respectively, for the X state, and 1.137 (1.135)/~ and 1.57 eV, respectively, for the A state (experimental values within parenthesis).
When a molecular equilibrium geometry is determined by minimizing the energy by a quasi-Newton-Ra... more When a molecular equilibrium geometry is determined by minimizing the energy by a quasi-Newton-Raphson method, the number of iterations required depends critically on the choice of an approximate molecular Hessian matrix. We find that a simple 15-parameter function ...
Chemical Physics Letters, 1996
It has recently been shown that Møller-Plesset perturbation calculations may diverge for single c... more It has recently been shown that Møller-Plesset perturbation calculations may diverge for single configuration dominated systems in extended basis sets. We examine the origin of this divergence using the neon atom as a test example. The lowest energies for total symmetric states are calculated for values of the perturbation parameter strength zϵ[−1, 1]. For z ≈ (−0.9)−(−0.8) avoided crossings between
Journal of The American Chemical Society, 2006
Fundamental World of Quantum Chemistry, 2003
Theoretical Chemistry Accounts: Theory, Computation, and Modeling (Theoretica Chimica Acta), 2004
... Savin [7] and Gra®fenstein and Cremer [8] have formulated theories which combine DFT with a m... more ... Savin [7] and Gra®fenstein and Cremer [8] have formulated theories which combine DFT with a multiconfigurational description of the wave ... Sergey Gusarov, Per-A˚ke Malmqvist, Roland Lindh, Bjo®rn O. Roos Department of Theoretical Chemistry, Chemical Center, POBox 124 ...
Theoretica Chimica Acta, 1990
Generally contracted basis sets for first row atoms have been constructed using the Atomic Natura... more Generally contracted basis sets for first row atoms have been constructed using the Atomic Natural Orbital (ANO) approach, with modifications for allowing symmetry breaking and state averaging. The ANOs are constructed by averaging over several atomic states, positive and negative ions, and atoms in an external electric field. The contracted basis sets give virtually identical results as the corresponding uncontracted sets for the atomic properties, which they have been designed to reproduce. The design objective has been to describe the ionization potential, the electron affinity, and the polarizability as accurately as possible. The result is a set of well-balanced basis sets for molecular calculations.
The Journal of Physical Chemistry A, 2008
New basis sets of the atomic natural orbital (ANO) type have been developed for the lanthanide at... more New basis sets of the atomic natural orbital (ANO) type have been developed for the lanthanide atoms La-Lu. The ANOs have been obtained from the average density matrix of the ground and lowest excited states of the atom, the positive ions, and the atom in an electric field. Scalar relativistic effects are included through the use of a Douglas-Kroll-Hess Hamiltonian. Multiconfigurational wave functions have been used with dynamic correlation included using second-order perturbation theory (CASSCF/CASPT2). The basis sets are applied in calculations of ionization energies and some excitation energies. Computed ionization energies have an accuracy better than 0.1 eV in most cases. Two molecular applications are included as illustration: the cerium diatom and the LuF3 molecule. In both cases it is shown that 4f orbitals are not involved in the chemical bond in contrast to an earlier claim for the latter molecule.
The Journal of Physical Chemistry A, 2005
New basis sets of the atomic natural orbital (ANO) type have been developed for the first, second... more New basis sets of the atomic natural orbital (ANO) type have been developed for the first, second, and third row transition metal atoms. The ANOs have been obtained from the average density matrix of the ground and lowest excited states of the atom, the positive and negative ions, and the atom in an electric field. Scalar relativistic effects are included through the use of a Douglas-Kroll-Hess Hamiltonian. Multiconfigurational wave functions have been used with dynamic correlation included using second order perturbation theory (CASSCF/CASPT2). The basis sets are applied in calculations of ionization energies, electron affinities, and excitation energies for all atoms and polarizabilities for spherically symmetric atoms. These calculations include spin-orbit coupling using a variation-perturbation approach. Computed ionization energies have an accuracy better than 0.2 eV in most cases. The accuracy of computed electron affinities is the same except in cases where the experimental values are smaller than 0.5 eV. Accurate results are obtained for the polarizabilities of atoms with spherical symmetry. Multiplet levels are presented for some of the third row transition metals.
The Journal of Physical Chemistry A, 2001
The structure and vibrational frequencies of the UO 2 molecule have been determined using multico... more The structure and vibrational frequencies of the UO 2 molecule have been determined using multiconfigurational wave functions (CASSCF/CASPT2), together with a newly developed method to treat spin-orbit coupling. The molecule has been found to have a (5fφ)(7s), 3 Φ u , Ω ) 2 ground state with a U-O bond distance of 1.77 Å. The computed antisymmetric stretching σ u frequency is 923 cm -1 with a 16/18 isotope ratio of 1.0525 which compares with the experimental values of 915 cm -1 and 1.0526, respectively. Calculations of the first adiabatic ionization energy gave the value 6.17 eV, which is 0.7 eV larger than the currently accepted experimental result. Reasons for this difference are suggested.
The Journal of Physical Chemistry A, 2004
New basis sets of the atomic natural orbital (ANO) type have been developed for the main group an... more New basis sets of the atomic natural orbital (ANO) type have been developed for the main group and rare gas atoms. The ANO's have been obtained from the average density matrix of the ground and lowest excited states of the atom, the positive and negative ions, and the dimer at its ...
Physical Chemistry Chemical Physics, 2000
Page 1. On the low-lying singlet excited states of styrene: a theoretical contribution¤ Vicent Mo... more Page 1. On the low-lying singlet excited states of styrene: a theoretical contribution¤ Vicent Molina,a Manuela O. Roosb and Malmqvistb Mercha n,a Bjo rn Per-A ke a Departamento de Universitat de Dr. Moliner 50, Burjassot, E-46100 Qu• mica F• sica, V ale`ncia, ...
Molecular Physics, 2004
... Sergey Gusarov, Per-Åke Malmqvist * & Roland Lindh pages 2207-221... more ... Sergey Gusarov, Per-Åke Malmqvist * & Roland Lindh pages 2207-2216. ... Colle, R and Salvetti, O. 1990. J. chem. Phys. , 93: 534 [CrossRef], [Web of Science ®] View all references15]15. Pollet, P, Savin, A, Leininger, T and Stoll, H. 2002. J. chem. Phys. ...
Journal of Chemical Theory and Computation, 2008
The electronic structure and low-lying electronic states of a Co(III)(diiminato)(NPh) complex hav... more The electronic structure and low-lying electronic states of a Co(III)(diiminato)(NPh) complex have been studied using multiconfigurational wave function theory (CASSCF/CASPT2). The results have been compared to those obtained with density functional theory. The best agreement with ab initio results is obtained with a modified B3LYP functional containing a reduced amount (15%) of Hartree-Fock exchange. A relativistic basis set with 869 functions has been employed in the most extensive ab initio calculations, where a Cholesky decomposition technique was used to overcome problems arising from the large size of the two-electron integral matrix. It is shown that this approximation reproduces results obtained with the full integral set to a high accuracy, thus opening the possibility to use this approach to perform multiconfigurational wave-function-based quantum chemistry on much larger systems relative to what has been possible until now.
The Journal of Chemical Physics, 1992
The recently implemented second-order perturbation theory based on a complete active space self-c... more The recently implemented second-order perturbation theory based on a complete active space self-consistent field reference function has been extended by allowing the Fock-type oneelectron operator, which defines the zeroth-order Hamiltonian to have nonzero elements also in nondiagonal matrix blocks. The computer implementation is now less straightforward and more computer time will be needed in obtaining the second-order energy. The method is illustrated in a series of calculations on N 2 , NO, 02' CH 3 , CH 2 , and F-.
The Journal of Chemical Physics, 2009
A general expression for the distribution of the fluctuating 2 ᐉ -pole moment M ᐉ of a spherical ... more A general expression for the distribution of the fluctuating 2 ᐉ -pole moment M ᐉ of a spherical sample of dielectric material is derived on the basis of dielectric theory combined with statistical mechanics. The formulas are compared with results from computer simulations of a weakly coupled Stockmayer fluid and the agreement is shown to be excellent. Furthermore, we calculate the size of the coupling, quantified through the free energy of solvation A solv , of the fluctuating electric moments to a surrounding dielectric medium. It turns out that the contribution to A solv from each fluctuating electric moment actually increases with increasing order ᐉ of the moment, resulting in a formally infinite free energy of solvation. We also present a correction to A solv for molecular media, which shows that the molecular nature of the surrounding medium effectively suppresses the divergence in the solvation free energy.
International Journal of Quantum Chemistry, 2009
Previous studies on photo dissociation of iodobenzene by Bersohn 1, El-Sayed 24, Smalley 5 and L... more Previous studies on photo dissociation of iodobenzene by Bersohn 1, El-Sayed 24, Smalley 5 and Leone 6 revealed two distinct mechanisms: a direct dissociation caused by an excitation to the anti bonding n−σ* state, and a pre dissociative mechanism, where the initial ...
Inorganic Chemistry, 2007
Uranium atoms activate methane upon ultraviolet excitation to form the methyl uranium hydride CH3... more Uranium atoms activate methane upon ultraviolet excitation to form the methyl uranium hydride CH3-UH, which undergoes alpha-H transfer to produce uranium methylidene dihydride, CH2=UH2. This rearrangement most likely occurs on an excited-quintet potential-energy surface and is followed by relaxation in the argon matrix. These simple U+CH4 reaction products are identified through isotopic substitution (13CH4, CD4, CH2D2) and density functional theory frequency and structure calculations for the strong U-H stretching modes. Relativistic multiconfiguration (CASSCF/CASPT2) calculations substantiate the agostic distorted C1 ground-state structure for the triplet CH2=UH2 molecule. We find that uranium atoms are less reactive in methane activation than thorium atoms. Our calculations show that the CH2=UH2 complex is distorted more than CH2=ThH2. A favorable interaction between the low energy open-shell U(5f) sigma orbital and the agostic hydrogen contributes to the distortion in the uranium methylidene complexes.
ChemPhysChem, 2007
The computation of the electronic g tensor by two multireference methods is presented and applied... more The computation of the electronic g tensor by two multireference methods is presented and applied to a selection of molecules including CN, BO, AlO, GaO, InO, ZnH, ZnF, O(2), H(2)O(+), O(3) (-), and H(2)CO(+) (group A) as well as TiF(3), CuCl(4) (2-), Cu(NH(3))(4) (2+), and a series of d(1)-MOX(4) (n-) compounds, with M=V, Cr, Mo, Tc, W, Re and X=F, Cl, Br (group B). Two approaches are considered, namely, one in which spin-orbit coupling and the Zeeman effect are included using second-order perturbation theory and another one in which the Zeeman effect is added through first-order degenerate perturbation theory within the ground-state Kramers doublet. The two methods have been implemented into the MOLCAS quantum chemistry software package. The results obtained for the molecules in group A are in good agreement with experiment and with previously reported calculated g values. The results for the molecules in group B vary. While the g values for the d(1) systems are superior to previous theoretical results, those obtained for the d(9) systems are too large compared to the experimental values.