Combined Hartree Fock Research Articles

Developments in molecular electronic structure evaluation based on the self-frictional field with Slater-type orbitals

Molecular electronic structure evaluations are investigated here using complete orthonormal sets of Guseinov $$\psi^{\left( \alpha \right)}$$ exponential-type orbitals ( $$\psi^{\left( \alpha \right)}$$ ETOs), where $$\alpha = 1,0, - 1, - 2, \ldots$$ is the self-friction quantum number. Using two-center overlap integrals over Slater-type orbitals (STOs) with same screening constants, all the one- and two-electron multicenter integrals are reformulated with the help of the Lowdin alpha radial function. The proposed formula yields useful definitions that enable us to evaluate the multicenter integrals and related combined Hartree–Fock–Roothaan equations over STOs. In terms of the self-frictional field effect, the effectiveness of the method is demonstrated using the BH3 molecule as an example application. The results of the calculation are validated using existing methods.

BIASING FIELD EFFECTS ON ELECTRONIC PROPERTIES IN HALOGENATED PHENYLENE ETHYNYLENE OLIGOMERS

In this paper results from ab initio simulations of the electronic structure properties of a class of halogenated phenylene ethynylene oligomers (OPE) are presented. These molecular species are investigated because of their suitable properties for application as single-molecule switches in the future emerging molecular electronic devices. Combined Hartree-Fock and Density Functional Theory approach is applied to investigate the biasing field effects on the relevant electronic properties, such as potential energy of the ground states, potential barrier height, localization of frontier molecular orbitals and the HOMO-LUMO gap. Special attention is also paid on the effects of substitution of the hydrogen atoms in the central phenylene ring of basic OPE molecule with halogen atoms. The analyses of the obtained results undoubtedly show that the biasing field has a strong impact on the potential barrier height, transition probabilities and band gap. Halogenation of the central phenylene ring does not have such a strong influence on the aforementioned properties, but it could be a useful way for fine tuning of some of the properties, especially the potential barrier height, enabling control of the torsional stochastic switching, inherent for the studied species.

Unified Treatment of One-Range Addition Theorems for Complete Orthonormal Sets of Generalized Exponential-Type Orbitals and Noninteger n Slater Functions

Abstract By the use of L(pl*)-generalized Laguerre polynomials (L(pl*)-GLPs) introduced by the author, the combined formulas for the one- and two-center one-range addition theorems of complete orthonormal sets of φ (pl*)-generalized exponential-type orbitals (φ (pl*)-GETOs) and χ-noninteger n Slater type orbitals (χ-NISTOs) in terms of χ-integer STOs (χ-ISTOs) are suggested, where pl* = 2l + 2 − α* and α* are the integer (α* = α, −∞ < α ≤ 2) or noninteger (α* ≠ α, −∞ < α* < 3) self-frictional quantum numbers. The series expansion coefficients of these theorems are expressed through the overlap integrals over χ-NISTOs. As an application, the Combined Hartree–Fock–Roothaan (CHFR) total energy values for the ground states of some atoms obtained in the minimal basis set approximation are presented.

Use of combined Hartree–Fock–Roothaan theory in evaluation of lowest states of K[Ar]4s 03d 1 and Cr + [Ar]4s 03d 5 isoelectronic series over noninteger n-Slater type orbitals

By the use of integer and noninteger n-Slater Type Orbitals in combined Hartree-Fock-Roothaan method, self consistent field calculations of orbital and lowest states energies have been performed for the isoelectronic series of open shell systems K [Ar]4s^0 3d^1 2(D) (Z=19-30) and Cr+ [Ar] 4s^0 3d^5 6(S) (Z=24-30). The results of calculations for the orbital and total energies obtained from the use of minimal basis sets of integer- and noninteger n-Slater Type Orbitals are given in tables. The results are compared with the extended-basis Hartree-Fock computations. The orbital and total energies are in good agreement with those presented in the literature. The results are accurately and considerably can be useful in the application of non-relativistic and relativistic combined Hartree-Fock-Roothaan approach for heavy atomic systems.

Use of noninteger n‐Slater type orbitals in combined Hartree–Fock–Roothaan theory for calculation of isoelectronic series of atoms Be to Ne

AbstractThe ground state calculations in the combined Hartree–Fock–Roothaan approach are performed for the neutral and the first 20 cationic members of the isoelectronic series of atoms from Be to Ne using noninteger n‐Slater type orbitals. For the total energies obtained, only a small deviation has been found. At the same time, the size of the present noninteger n‐Slater type orbitals is smaller than that of the usual extended integer n‐Slater functions in literature. All of the nonlinear parameters are fully optimized. The relationship between optimized parameters and atomic number Z is also investigated. For each atom, the total energies are given in tables. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009

Application of combined Hartree–Fock–Roothaan theory to molecules with arbitrary number of closed and open shells

In this study, the applicability of the combined Hartree–Fock–Roothaan (CHFR) theory of atomic-molecular and nuclear systems (Guseinov, J Math Chem 42:177, 2007) to the molecules is demonstrated using minimal basis set of Slater type orbitals (STO). As an example of application of CHFR theory, the calculations have been performed for the ground state of electronic configuration of methylene molecule CH2 which has two open shells. The results of computer calculations for the orbital, kinetic and total energies, linear combination coefficients of symmetrized molecular orbitals and virial ratios are presented.

Combined Open Shell Hartree–Fock Theory of Atomic–Molecular and Nuclear Systems

In this study, the combined Hartree–Fock (HF) and Hartree–Fock–Roothaan equations are derived for multideterminantal single configuration states with any number of open shells of atoms, molecules and nuclei. It is shown that the postulated orbital-dependent energy and Fock operators are invariant to the unitary transformation of orbitals. This new methodology is based entirely on the spin-restricted HF theory. As an application of combined open shell theory of atomic–molecular and nuclear systems presented in this paper, we have solved Hartree–Fock–Roothaan equations for the ground state of electronic configuration C(1s 22s 22p 2) using Slater type orbitals as a basis.

Density-functional theory and hybrid density-functional theory continuum solvation models for aqueous and organic solvents: universal SM5.43 and SM5.43R solvation models for any fraction of Hartree-Fock exchange

Hybrid density functional theory, which is a combined Hartree–Fock and density functional method, provides a simple but effective way to incorporate nonlocal exchange effects and static and dynamical correlation energy into an orbital-based theory with affordable computational cost for many important problems of gas-phase chemistry. The inclusion of a reaction field representing an implicit solvent in a self-consistent hybrid density functional calculation provides an effective and efficient way to extend this approach to problems of liquid-phase chemistry. In previous work, we have parameterized several models based on this approach, and in the present article, we present several new parameterizations based on implicit solvation models SM5.43 and SM5.43R. In particular, we extend the applicability of these solvation models to several combinations of the MPWX hybrid-density functional with various one-electron basis sets, where MPWX denotes a combination of Barone and Adamo’s modified version of Perdew and Wang’s exchange functional, Perdew and Wang’s correlation functional, and a percentage X of exact Hartree–Fock exchange. SM5.43R parameter optimizations are presented for the MPWX/MIDI!, MPWX/MIDI!6D, and MPWX/6-31+G(d,p) combinations with X=0 (i.e., pure density functional theory), 25, 42.8, and 60.6, and for MPWX/6-31G(d) and MPWX/6-31+G(d), with X=0, 42.8, and 60.6; this constitutes a total of 18 new parameter sets. [Note that parameter optimizations using MPW25/6-31G(d) and MPW25/6-31+G(d) were carried out in a previous SM5.43R parameterization.] For each of the five basis sets, we found no significant loss in the accuracy of the model when parameters averaged over the four values of X are used instead of the parameters optimized for a specific value of X. Therefore for each of the five basis sets used here, the SM5.43R and SM5.43 models are defined to have a single parameter set that can be used for any value of X between 0 and 60.6. The new models yield accurate free energies of solvation for a broad range of solutes in both water and organic solvents. On the average, the mean-unsigned errors, as compared with those from experiment, of the free energies of solvation of neutral solutes range from 0.50 to 0.55 kcal/mol and those for ions range from 4.5 to 4.9 kcal/mol. Since the SM5.43R model computes the free energy of solvation as a sum of bulk-electrostatic and non-bulk-electrostatic contributions, it may be used for detailed analysis of the physical effects underlying a calculation of the free energy of solvation. Several calculations illustrating the partitioning of these contributions for a variety of solutes in n-hexadecane, 1-octanol, and water are presented.

Combined Hartree–Fock quantum mechanical and molecular mechanical molecular dynamics simulations of water at ambient and supercritical conditions

Combined ab initio Hartree–Fock quantum mechanical/molecular mechanical (QM/MM) molecular dynamics simulations have been carried out for water at ambient and supercritical conditions. The QM/MM coupling potential is optimized for ambient water by scaling down the original MM charges in the MM potential model. Simulation results show that the modified QM/MM coupling potential behaves well in the studied water system. The evolution of the water structure from ambient to the supercritical conditions is studied and compared to the available experimental results. Our simulation results suggest that, at supercritical conditions, the data refined from the experiment by neutron diffraction with the isotopic substitution technique probably overestimate the hydrogen bonding interactions.

On the structure of polaronic defects in thiophene oligomers: a combined Hartree–Fock and Density Functional Theory study

Thiophene oligomer radical cations were studied as model for the polaronic defects in doped polythiophenes. Oligomers of increasing size (2 to 10 rings) were characterized by means of ab initio calculations. Optimized geometries and charge distributions were computed at both the Hartree–Fock (HF) and Density Functional Theory (DFT) levels. When electron correlation is taken into account the whole shape of the polaronic defect changes so that the self-localization of the positive charge and the corresponding quinoid structural distortion are greatly reduced. The energetics of the aromatic vs. quinoid geometry is investigated using substituted bithiophenes as model compounds. The discrepancy between HF and DFT results is confirmed. Traditional post-HF approach is found to agree with DFT.

Effect of argon atoms on charge distributions in small lithium clusters.

Charge distributions in lithium clusters ${\mathrm{Li}}_{\mathit{n}}$ (n=3,4,5) embedded into a matrix of argon atoms have been computed by means of a combined Hartree-Fock and density-functional-theory approach. The positions of the argon atoms, found using molecular-dynamics techniques, points to the origins of pseudopotential locations. We show that charge alterations in ${\mathrm{Li}}_{\mathit{n}}$ may be as high as 0.2e, reflecting local changes in the environment.

Combined Hartree-Fock and density functional theory: a distributed memory parallel implementation

The parallelisation of an ab initio, Kohn-Sham density functional code for direct SCF energy and gradient evaluation calculations is described. The implementation of the parallel Hartree-Fock method uses the PRISM algorithm for the calculation of the two-electron integrals. A Kohn-Sham density functional code has been written by us and interfaced to Gaussian 92. This code has also been parallelised and incorporated into a set of new ‘links’ for the Gaussian 92 package. The work, although performed using one particular type of workstation ‘cluster’ (the Hewlett-Packard 9000-7xx series), has been based upon P.V.M. (Parallel Virtual Machine), a portable communications package which is already available for a large number of systems including many UNIX workstations. The methods described are, thus, applicable to any system which is supported by both the Gaussian 92 program and the P.V.M. communications package with minimal changes required to the sequential code.

Is aluminum-argon (AlAr12) icosahedral?

The energy of AlAr 12 with a central aluminum atom is significantly lowered when the cluster distorts for icosahedral symmetry. A range of scenarios is possible, including loss of all symmetry. The Born-Oppenheimer surface for AlAr 12 is estimated using combined Hartree-Fock simulated annealing techniques. Also, the stability of high symmetry configurations and the possibility of nonadiabatic effects are explored in an approximate model based on a linear expansion in just three electronic states that are degenerate in icosahedral symmetry

Molecular properties of the boron trimer obtained by combined Hartree-Fock and density-functional calculations.

Hartree-Fock calculations on restricted regions of the ground-state potential-energy surface of ${\mathrm{B}}_{3}$ are carried out. The correlation energy is calculated by using one-body and two-body density functionals. The results obtained with all those functionals are very similar, predicting a stable molecule with a potential-energy surface that shows two minima that differ by about 1.3 eV. The present results are in good agreement with recent calculations of Hernandez and Simons [J. Chem. Phys. 94, 2961 (1991)], who used a very different method in which correlation energy is obtained by extended multiconfiguration calculations.