An efficient algorithm for energy gradients in valence bond theory with nonorthogonal orbitals is presented. A general Hartree-Fock-like expression for the Hamiltonian matrix element between valence bond (VB) determinants is derived by introducing a transition density matrix. Analytical expressions for the energy gradients with respect to the orbital coefficients are obtained explicitly, whose ...

A simple ten-parameter interatomic potential model is described that is capable of accurately reproducing the static and dynamical properties of complex oxides. The accuracy of this model stems from the crystal-chemical bond-valence theory of ionic and covalent bonding. The development of a specific variant of this model for ferroelectric PbTiO3 sPTd is discussed in detail, and comparison of th...

only two voices have been represented in italian grammar. if we look at the passive constructions from a pragmatic point of view, it can be seen as a language strategy being classified as an event. this change of perspective creates different structures. in this article we shall study a speaker’s change of perspective in attention to the valence theory. according to this theory, a verb on the b...

When two electrons occupy the same bond at the same time, they repel each other, and their motions are not perfectly independent. We consider two approaches: molecular orbital theory, which assumes electrons do not repel each other and move independently, and valence bond theory, which assumes electrons interact so strongly they cannot be on the same nuclei at the same time. The truth lies betw...

In this study, paraphenylenediamine was first bonded to the fullerene and was optimized geometrically by Using the quantum chemistry methods. paraphenylenediamine was examined in the isolated state and in the fullerene-bonded state via carbon atoms. In the theoretical research, the simulation was done by the Gauss View software. Then, the bonding orbital calculation was done by using the NBO me...

We consider the use in quantum Monte Carlo calculations of two types of valence bond wave functions based on strictly localized active orbitals, namely valence bond self-consistent-field and breathing-orbital valence bond wave functions. Complemented by a Jastrow factor, these Jastrow-valence-bond wave functions are tested by computing the equilibrium well depths of the four diatomic molecules ...