Hartee-Fock calculations

A calculation approach to this question is ongoing, but it has been noted that the conclusion depends on the level of approximation <1999JMT1>. According to Hartee-Fock calculations, the most stable structure of l,6,6aA-trithia-pentalene 175 has Cs symmetry, with the structure 8.7 or 10.7 kcal mol 1 higher in energy <1991JA6449>. 

Spectroscopic (MS, NMR, IR) studies of quinoxalines were conducted . The structure and vibrational spectra of 2,3-bis(2-pyridyl)quinoxaline (bpq) and 2(A -methylpyridyl)-3-pyridylquinoxaline (meppq) useful for building blocks for dendrimers were measured by crystal X-ray diffraction and IR spectral experiments, respectively <2002JMT(589/90)301>. Those results were compared with ones calculated from the ab initio Hartee-Fock and the hybrid density functional methods. 

Mukheijee et al [56] also used the half projected Hartee-Fock (HPHF) method due to Smeyers and co-workers [70-74], which is based on variational formulation with two DODS determinant for the representation of the wave function and is proved to be very effective in calculating singly excited states of molecules. Table 5 displays the energy values only in the cis and trans conformations of the two excited states. 

A b initio quantum chemical studies of hyperfine structures (hfs) were initiated some 25 years ago, with the pioneering work of Meyer and others [127]. However, results from the early Hartee-Fock-based methods deviated considerably from experimentally determined hf parameters. It was not until the configuration interaction (Cl) techniques were fully developed for hfs calculations, that theoretical predictions of high accuracy were possible for atomic and molecular radicals [20]. This is mainly associated with the importance of electron correlation and with the development of new and fax larger basis sets. In later years, hfs calculations have also been carried out with great success using various levels of multiconfiguration SCF (MCSCF) [21], multireference Cl (MRCI) [22] and coupled cluster (CC) theory [23]. 

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