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A molecular improved generator coordinate Hartree–Fock (HF) method is used to generate a highly accurate Gaussian basis set (GBS) for N2, BF, and CO molecules. This basis set contains 26s15p8d5f primitive Gaussian-type functions on each center. Our ground state HF total energies are near the HF limits, and are better than those obtained with a larger universal GBS (UGBS) (30s15p15d15f) and with specific GBSs of the same size (26s18p10d7f) for each molecule. Our second-order Møller–Plesset energy corrections are also better than the corresponding ones calculated with the larger UGBS. [Copyright &y& Elsevier]

A power series for total energies of molecules is derived using the previously-obtained series for the one-electron density matrix (DM) P [J. Mol. Struct. (Theochem) 343 (1995) 183] and the well-known relation between the energy E and the DM P (E=Trace (PH), where H is the Hamiltonian matrix). Two components are revealed within any correction E(k) of the new series so that one of them describes the kth order energy alteration due to charge redistribution and the another represents the analogous alteration owing to formation of additional bond orders vs. those of the system underlying the zero order Hamiltonian matrix. Molecular-structure-independent but k-dependent relations are established between the above-specified two components for k=0, 1, 2, 3, 4. These relations allow the total correction E(k) to be expressed in terms of charge transfer energy of respective order and thereby yield a general interdependence between the stabilization energy of a molecular system and the relevant charge redistribution for any number of participating orbitals and for any type of change in the structure of the system. Non-trivial consequences of this principal result of the paper also are revealed, in particular an interrelation between the trans-effect of substituent studied recently [J. Mol. Struct. (Theochem) 532 (2000) 257] and the well-known gauche- and cis-effects describing the most stable conformations of substituted alkanes and alkenes, as well as of related heteroatom-containing compounds. [Copyright &y& Elsevier]

The generator coordinate Hartree–Fock method is used to generate universal basis sets (UBSs) of Gaussian- and Slater-type functions for low-lying excited states of some mono-positive and -negative ions. From our basis sets the total energies are calculated and compared with the corresponding results obtained with other UBSs and with fully-optimized basis sets of STFs. [Copyright &y& Elsevier]

[Display omitted] • First attempt to describe substituent effects in terms of total energies. • Key quantity is the difference of total energies of para and meta conformers. • Total energy proved to be a useful quantity in studying substituent effects. This article is the first attempt to describe substituent effects in terms of total energies of the substituted derivatives of benzoic acid. The key quantity in this attempt is the difference of the total energies of the para and meta conformers. This quantity is then correlated with Hammett substituent constants and with some theoretical parameters of the electronic structure of the substituent. While it was previously unclear that the total energy of a molecule would prove to be a useful quantity in studying substituent effects, our research shows that, indeed, this energetical difference correlates well with other parameters if only they also relate to both of these conformers, that is they are differences of their individual counterparts determined for both of these conformers separately. [ABSTRACT FROM AUTHOR]