Two basis sets-a large and a small one-are associated with each nucleus of the system. Each atom has its own separate one-electron basis comprising the large basis set of the atom in question and the small basis sets for the partner atoms in the complex. The perturbed atoms in molecules and solids model is at core of the approach since it allows for the definition of perturbed atoms in a system. It ...

We develop a new scheme for evaluating different molecular integrals using Gaussian type orbitals. In this new scheme, the evaluation of integrals is performed in two steps during runtime. The first step is a top-down procedure that maps each recurrence relation into a jagged array (array of arrays), where each element of a member array represents either the final results or some intermediate integrals ...

The bonding in metals is analysed within the framework of the PATMOS (Perturbed AToms in MOlecules and Solids) model. The electronic binding energy per atom is written as a sum of a distortion energy of the atoms and the partitioned interaction energy comprising Coulombic, exchange and correlation terms. The adopted physical model of the infinite system, is spherical embedding of the atoms of the ...

A new computational method for electronic-structure studies of molecules and solids is presented. The key element in the new model – denoted the perturbed atoms in molecules and solids model – is the concept of a perturbed atom in a complex. The basic approximation of the new model is unrestricted Hartree Fock (UHF). The UHF orbitals are localized by the Edmiston-Ruedenberg procedure. The perturbed ...

The solution of the Liouville–von Neumann equation in the relativistic Dirac–Kohn–Sham density matrix formalism is presented and used to calculate X-ray absorption cross sections. Both dynamical relaxation effects and spin–orbit corrections are included, as demonstrated by calculations of the X-ray absorption of SF6 near the sulfur L2,3-edges. We also propose an analysis facilitating the interpretation ...