Fragment-localized Kohn-Sham orbitals via a Singles-CI procedure and application to local properties and intermolecular energy decomposition analysis (original) (raw)
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Journal of Chemical Theory and Computation, 2008
As for generating localized Hartree-Fock orbitals, we propose a potentially linearscaling singles-CI scheme to construct fragment-localized density functional theory (DFT) orbitals for molecular systems as water clusters. Due to the use of a deformation step instead of a localization step, the influence of the environment on each separate molecule can be studied in detail. The generated orbital set for the whole molecular system is strictly equivalent to a set of canonical orbitals and is a subsequent energy decomposition of intermolecular interactions into electrostatic, exchange repulsion, and orbital interaction, well beyond dimer systems. Beyond this, the correspondence of the individual orbitals to the initial monomer orbitals permits to assess how an interaction deforms an electron density. We show this for dipole moments, which may be decomposed into monomer contributions, polarization, and charge-transfer contribution. Applications to a water and an ammonia dimer and chains of water molecules show possible further developments toward multipolar expansions and other orbital-based schemes for parametrizing force fields.
New Orbital-Free Approach for Density Functional Modeling of Large Molecules and
2016
Development of the orbital-free (OF) approach of the density functional theory (DFT) may result in a power instrument for modeling of complicated nanosystems with a huge number of atoms. A key problem on this way is calculation of the kinetic energy. We demonstrate how it is possible to create the OF kinetic energy functionals using results of Kohn-Sham calculations for single atoms. Calculations provided with these functionals for dimers of sp-elements of the C, Si, and Ge periodic table rows show a good accordance with the Kohn-Sham DFT results.
Chemical Physics Letters, 2008
The Hartree-Fock density matrix is used to generate occupied and virtual molecular orbitals localized on a selected (active) region within a molecule. The orbitals are well suited for high level description of electron correlation in the active site. Orbitals outside the active site are not constructed explicitly, they provide a frozen core for the correlation calculation. Standard correlation methods are straightforward to apply and result local correlation energies. Transforming to locally canonical orbitals facilitates an iteration-free evaluation of local Møller-Plesset(MPn) energies. Selection of active orbitals does not produce dangling bonds since no chemical bonds are cut at the boundary.
Generalized Hybrid-Orbital Method for Combining Density Functional Theory with Molecular Mechanicals
ChemPhysChem, 2005
The generalized hybrid orbital (GHO) method has previously been formulated for combining molecular mechanics with various levels of quantum mechanics, in particular semiempirical neglect of diatomic differential overlap theory, ab initio Hartree-Fock theory, and self-consistent charge density functional tight-binding theory. To include electron-correlation effects accurately and efficiently in GHO calculations, we extend the GHO method to density functional theory in the generalized-gradient approximation and hybrid density functional theory (denoted by GHO-DFT and GHO-HDFT, respectively) using Gaussian-type orbitals as basis functions. In the proposed GHO-(H)DFT formalism, charge densities in auxiliary hybrid orbitals are included to calculate the total electron density. The orthonormality constraints involving the auxiliary Kohn-Sham orbitals are satisfied by carrying out the hybridization in terms of a set of Löwdin symmetrically orthogonalized atomic basis functions. Analytical gradients are formulated for GHO-(H)DFT by incorporating additional forces associated with GHO basis transformations. Scaling parameters are introduced for some of the one-electron integrals and are optimized to obtain the correct charges and geometry near the QM/MM boundary region. The GHO-(H)DFT method based on the generalized gradient approach (GGA) (BLYP and mPWPW91) and HDFT methods (B3 LYP, mPW1PW91, and MPW1K) is tested-for geometries and atomic chargesagainst a set of small molecules. The following quantities are tested: 1) the CC stretch potential in ethane, 2) the torsional barrier for internal rotation around the central CC bond in n-butane, 3) proton affinities for a set of alcohols, amines, thiols, and acids, 4) the conformational energies of alanine dipeptide, and 5) the barrier height of the hydrogenatom transfer between n-C 4 H 10 and n-C 4 H 9 , where the reaction center is described at the MPW1K/6-31G(d) level of theory.
New Orbital-Free Approach for Density Functional Modeling of Large Molecules and Nanoparticles
Modeling and Numerical Simulation of Material Science, 2015
Development of the orbital-free (OF) approach of the density functional theory (DFT) may result in a power instrument for modeling of complicated nanosystems with a huge number of atoms. A key problem on this way is calculation of the kinetic energy. We demonstrate how it is possible to create the OF kinetic energy functionals using results of Kohn-Sham calculations for single atoms. Calculations provided with these functionals for dimers of sp-elements of the C, Si, and Ge periodic table rows show a good accordance with the Kohn-Sham DFT results.
A density difference based analysis of orbital-dependent exchange-correlation functionals
Molecular Physics, 2014
We present a density difference based analysis for a range of orbital-dependent Kohn-Sham functionals. Results for atoms, some members of the neon isoelectronic series and small molecules are reported and compared with ab initio wave-function calculations. Particular attention is paid to the quality of approximations to the exchange-only optimized effective potential (OEP) approach: we consider both the Localized Hartree Fock as well as the Krieger-Li-Iafrate methods. Analysis of density differences at the exchange-only level reveals the impact the approximations have on the resulting electronic densities. These differences are further quantified in terms of the ground state energies, frontier orbital energy differences and highest occupied orbital energies obtained. At the correlated level an OEP approach based on a perturbative second-order correlation energy expression is shown to deliver results comparable with those from traditional wave function approaches, making it suitable for use as a benchmark against which to compare standard density-functional approximations.
A new density functional method for electronic structure calculation of atoms and molecules
arXiv: Chemical Physics, 2019
This chapter concerns with the recent development of a new DFT methodology for accurate, reliable prediction of many-electron systems. Background, need for such a scheme, major difficulties encountered, as well as their potential remedies are discussed at some length. Within the realm of non relativistic Hohenberg-Kohn-Sham (HKS) DFT and making use of the familiar LCAO-MO principle, relevant KS eigenvalue problem is solved numerically. Unlike the commonly used atom-centered grid (ACG), here we employ a 3D cartesian coordinate grid (CCG) to build atom-centered localized basis set, electron density, as well as all the two-body potentials directly on grid. The Hartree potential is computed through a Fourier convolution technique via a decomposition in terms of short- and long-range interactions. Feasibility and viability of our proposed scheme is demonstrated for a series of chemical systems; first with homogeneous, local-density-approximated XC functionals followed by non-local, gradi...
Density Functional Treatment of Interactions and Chemical Reactions at Interfaces
This chapter reviews recent applications of density functional theory (DFT) based methods in the study of the interaction of small gaseous molecules with metal nanoparticles, metal surfaces, and porous or biological materials and applications in the study of chemical reactions at catalytic sites of transition metals or enzymes. Focus is given to the interaction of small molecules, e.g. H 2 O, O 2 , CO, CO 2 , etc., with the scaffold atoms of metal organic frameworks (MOF) or with zeolites, in the field of gas adsorption, or with the exposed atoms on transition metal surfaces or nanoparticles, in the field of heterogeneous catalysis, and to the interaction of small organic molecules with the capacity to inhibit a catalytic cysteine of the Malaria's parasite, in the field of drug design. The roles of undercoordinated atoms on the strength of the interaction and of the type of the exchangecorrelation functional considered for the calculations are analyzed. Finally, recent successes of the consideration of DFT based approaches to study, with atomic detail, the reactions of such molecules on these materials are also reviewed.
The Journal of chemical physics, 2015
Analytic second derivatives of the energy with respect to nuclear coordinates have been developed for spin restricted density functional theory (DFT) based on the fragment molecular orbital method (FMO). The derivations were carried out for the three-body expansion (FMO3), and the two-body expressions can be obtained by neglecting the three-body corrections. Also, the restricted Hartree-Fock (RHF) Hessian for FMO3 can be obtained by neglecting the density-functional related terms. In both the FMO-RHF and FMO-DFT Hessians, certain terms with small magnitudes are neglected for computational efficiency. The accuracy of the FMO-DFT Hessian in terms of the Gibbs free energy is evaluated for a set of polypeptides and water clusters and found to be within 1 kcal/mol of the corresponding full (non-fragmented) ab initio calculation. The FMO-DFT method is also applied to transition states in SN2 reactions and for the computation of the IR and Raman spectra of a small Trp-cage protein (PDB: 1L...