Hartree-Fock calculations generalization

In general, DFT calculations proceed in the same way as Hartree-Fock calculations, with the addition of the evaluation of the extra term, This term cannot be evaluated analytically for DFT methods, so it is computed via numerical integration. 

Tupitsyn, I. I. and Mosyagin, N. S. grecp/hfj 1995. Program for atomic finite-difference two-component Hartree-Fock calculations with the generalized RECP in the //-coupling scheme. 

Both intramolecular force constants are lowered somewhat through complex formation (Table 6). As expected this effect is larger in the proton-donor than in the proton-acceptor molecule. In Table 7 we present calculated and experimental data on the vibrational spectrum of (HF)2. General agreement is obtained. The most remarkable feature is the strict separation of intra- and intermolecular modes on the frequency axis. Hydrogen bond formation is a weak interaction compared to the formation of a chemical bond hence, the normal frequencies are well separated. However, Hartree-Fock calculations of bond stretching force constants... 

The numerical values for these quantities have been extracted and summarized in Table V. These results did not surprise us, since they were predicted by ionic model calculations (19) as well as one ab initio Hartree-Fock calculation for lithium fluoride (20) (a subsequent one is also shown in Table V) which treated both monomer and dimer. However, the trend is opposite to that observed with metal and noble gas dimers, whose I.P. s are lower than the corresponding monomers. It is simply a consequence of the relative bonding strengths of the two units in the neutral and ionic forms. Alakll halide dimers are more stable as neutrals metal and noble gas dimers are generally more stable as ions. 

MINDO is a much more powerful theory when properly parametrized, giving generally better predictions of structures and energies than minimum-basis-set Hartree-Fock calculations. We shall later describe applications of MINDO and similar approaches to borates (Uchida et al., 1985) and to defects in Si02 (Edwards and Fowler, 1985). However, some of the claims made for this semiempirical approach have been strongly criticized (e.g., Pople, 1975). 

A general term used to refer to calculations from first principles, often describing Hartree-Fock calculations with no integral approximations and with self-consistent charge distributions... 

In general, Hartree-Fock calculations on molecules give molecular orbitals (MOs) that extend (i.e., are delocalized) over the entire molecular framework. These so-called canonical MOs (CMOs) may be transformed into localized orbitals, such as NBOs. Technically, the Fock matrix in the basis of CMOs is con-... 

Quantum mechanical calculations are carried out using the Variational theorem and the Har-tree-Fock-Roothaan equations.t - Solution of the Hartree-Fock-Roothaan equations must be carried out in an iterative fashion. This procedure has been called self-consistent field (SCF) theory, because each electron is calculated as interacting with a general field of all the other electrons. This process underestimates the electron correlation. In nature, electronic motion is correlated such that electrons avoid one another. There are perturbation procedures whereby one may carry out post-Hartree-Fock calculations to take electron correlation effects into account. " It is generally agreed that electron correlation gives more accurate results, particularly in terms of energy. 

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