The comparisons shown in Tables 5 and 6 indicate that the DFT methods may predict good results when these are compared to experimental values, however, it can also be seen that these methods provide only a small improvement over the Hartree-Fock method, as can be observed in the 13C data where the chemical shifts are too deshielded with respect to the experimental values.
The first class of methods are the quantum chemistry methods, the simplest of which, the Hartree-Fock method, is too crude an approximation for most problems of interest.
Restricted Hartree-Fock method was used, where the molecule is a closed shell system with all orbitals doubly occupied.
Geometry optimizations were done using the unrestricted Hartree-Fock method with the 6-31G(d) basis set.
Gaussian basis sets (24s14p, 30s19p14d, and 33s21p14d for O (3P), Ti (5S), and Ba (1S) atoms, respectively), are designed with the strategy of the Generator Coordinate Hartree-Fock method.
Using the Hartree-Fock method with the 6-31G∗ baset set we have calculated structures, vibrational frequencies, and bond strengths for the isolated HMX molecule and its two major reaction products.
The Hartree-Fock method was used for NMR chemical shielding calculations.
The unrestricted Hartree-Fock method overestimates the charge localization due to the neglect of electron correlation effects [49].
The resonating Hartree-Fock method proposed by Fukutome utilizes nonorthogonal SDs, and many noteworthy results have been reported [25 30].
The main methods of studying the electronic properties of atomic clusters are quantum mechanics methods, such as restricted and unrestricted Hartree-Fock method, the density functional theory, and molecular dynamics.
