The computational complexity of ab initio electronic structure methods can be decreased through the so-called density fitting scheme. The density fitting scheme is also known as resolution of identity (RI). Density fitting schemes became a popular approach to approximate the four-centre two-electron integrals which appear in the computation of the Fock matrix in the Hartree-Fock (HF) method. In...

The properties of hot matter are studied in the frame of the relativistic Brueckner-Hartree-Fock theory. The equations are solved self-consistently in the full Dirac space. For the interaction we used the potentials given by Brockmann and Machleidt. The obtained critical temperatures are smaller than in most of the nonrelativistic investigations. We also calculated the thermodynamic properties ...

For neutral atoms and molecules and positive ions and radicals, we prove the existence of solutions of the Hartree-Fock equations which minimize the Hartree-Fock energy. We establish some properties of the solutions including exponential falloff.

Structural and magnetic properties of purine and pyrimidine nucleotides (CMP, UMP, dTMP, AMP, GMP, IMP) were studied at different levels of ab initio molecular orbital theory. These calculations were performed at the hartree-fock level and density functional B3LYP methods. Geometries were fully optimized by following Cs symmetry restrictions. The standard 6-31G** basis set which includes polari...

dppc (dipalmitoylphosphatidylcholine) and dmpc (dimyristoylphosphatidylcholine) are taken asphospholipids with an equal polar heads and with the difference in the length of hydrocarbonchains. results obtain from the structural optimization of the isolated dppc and dmpc in the gasphase, at the hartree-fock level of theory by means of sto-3g,3-21g, 6-31g and 6-31g* basissets. the most important d...

A quantum-chemical study on the consequences of geometric modification and chelation on the electronic structure and optical properties of a tetra(carboxylic acid)phenyleneethynylene dye, of interest for chemical sensing applications, is presented. Rotation within the central biphenylene and complexation with divalent metal ions--in particular Cu2+--lead to notable changes in the absorption and...

It is typically assumed that once a Hartree-Fock (HF) reference wave function is determined, the correlated wave function obtained from that HF wave function describes the same electronic state. In this paper, we report the appearance of multiple CCSD solutions obtained from the UHF reference wave function for the known ground state of a chemically interesting molecule, NiH. To determine a corr...

Hartree-Fock (HF) method is a useful first-step tool for investigating electronic structure and total energy of atoms and molecules: it gives very good electron density, reasonably accurate total energy, and molecular orbitals and orbital energies that are helpful for understanding the electronic structure. The HF method is, however, not commonly applied to solids nowadays, since electronic scr...

Two combined quantum mechanics/molecular mechanics (QM/MM) molecular dynamics simulations, namely, HF/MM and B3LYP/MM, have been performed to investigate the local structure and dynamics of liquid ammonia. The most interesting region, a sphere containing a central reference molecule and all its nearest surrounding molecules (first coordination shell), was treated by the Hartree-Fock (HF) and hy...

Pariser-Parr-Pople (P-P-P) model Hamiltonian is employed frequently to study the electronic structure and optical properties of π-conjugated systems. In this paper we describe a Fortran 90 computer program which uses the P-P-P model Hamiltonian to solve the Hartree-Fock (HF) equation for infinitely long, onedimensional, periodic, π-electron systems. The code is capable of computing the band str...