Cálculo de la fuerza electrostática generada en posiciones nucleares para sistemas diatómicos, a partir de funcionales aproximados para la energía cinética

Abstract

This work analyses the behaviour of the approximate kinetic energy functional, TSLYP+Z [r], in the vicinity of the nucleus. The electrostatic force for the simplest diatomic system, H2, is calculated in the framework of the Bohr-Oppenheimer approximation. A combination of functional PBE2 with the functional LP97 is used to correct the behavior of the latter near the nuclei. The PBE2 functional is obtained easily by applying the conjointness criterion to an exchange functional. Thus a non-interacting kinetic energy functional can be generated, such as PBE2, which has a good behavior near the nucleus but an inadequate behavior in other regions. The combination of the two functionals contains a weight function ranging from 1 (next to the core) to 0 at infinity. In this way near the nucleus the kinetic energy and behaves like PBE2 and away from the nucleus as the functional LP97. The weight function is a decreasing exponential with parameter α which can be optimized to obtain the correct value of the bond length.