Density functional theory (DFT) is often used to determine the electronic and geometric structures of molecules. While studying alkynyl radicals, we discovered that DFT exchange-correlation (XC) functionals containing less than ∼22% Hartree-Fock (HF) exchange led to qualitatively different structures than those predicted from ab initio HF and post-HF calculations or DFT XCs containing 25% or mo...

We compare two different approaches to investigations of many-electron systems. The first one is the Hartree-Fock (HF) method and the second one is the Density Functional Theory (DFT). Overview of the main features and peculiar properties of HF method is presented. We discuss a way to realize the HF method within the Kohn-Sham (KS) theory and show that it is impossible without including a speci...

Density functional theory(DFT) and Hartree-Fock(HF) calculations are reported for the family of transition metal fluorides ScF3, TiF4, VF5, and CrF6. Both HF and the local-density-aproximation (LDA) yield excellent agreement with experimental bond lengths, while the B-LYP gradient-corrected density functional gives bond lengths 0.04 − 0.05 Å too long. An investigation of various combinations of...

When using quantum chemistry techniques to calculate the energetics of bulk crystals, there is a need to calculate the Hartree-Fock (HF) energy of the crystal at the basis-set limit. We describe a strategy for achieving this, which exploits the fact that the HF energy of crystals can now be calculated using pseudopotentials and plane-wave basis sets, an approach that permits basis-set convergen...

We present the Hartree-Fock approximation method for the many-body problems in Quantum Mechanics cor r esponding to the interaction of neutrons and protons We study the vanous farms of Hartree-Fock équations, the questions related to spin-dependence and spin-orbtt forces, symmetries of the nucleus and symmetry breakings and time-dependent Hartree-Fock équations AMS (MOS) Subject Classifications...

The direct ~recomputation of two-electron integrals! implementation of the gauge-including atomic orbital ~GIAO! and the CSGT ~continuous set of gauge transformations! methods for calculating nuclear magnetic shielding tensors at both the Hartree-Fock and density functional levels of theory are presented. Isotropic C, N, and O magnetic shielding constants for several molecules, including taxol ...

This study involves the synthesis of title molecule 1H-IMAP, characterized by using FT-IR spectrum and theoretical calculation optimized geometrical parameters most stable structure 1H-IMAP computation its vibrational frequencies Hartree-Fock(HF) method basis sets 6-31G(d,p), HF/6-311G(d,p) Density functional theory (DFT) set B3LYP/6-31G(d,p) has been made Gaussion 03 software compared both exp...

Infrared (IR) and ultraviolet (UV) spectroscopic analysis of eight structural isomers of C20 carbon nanostructures, i.e. ring, tadpole, bow-tie, dumb-bell, spiro, propellane, bowl and cage, were performed at different levels of theory including semi-empirical (AM1 and PM3), Hartree-Fock (HF/6-31++G, 6-31++G**) and density functional theory (B3LYP/6-31++G, 6-31++G**). A broad range of IR spectra...

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 ...