Non-Born–Oppenheimer study of positronic molecular systems: e+LiH

Abstract

Very accurate non-Born-Oppenheimer variational calculations of the ground state of e ϩ LiH have been performed using explicitly correlated Gaussian functions with preexponential factors dependent on powers of the internuclear distance. In order to determine the positron detachment energy of e ϩ LiH and the dissociation energy corresponding to the e ϩ LiH fragmentation into HPs and Li ϩ we also calculated non-BO energies of HPs, LiH, and Li ϩ . For all the systems the calculations provided the lowest ever-reported variational upper-bounds to the ground state energies. Annihilation rates of HPs and e ϩ LiH were also computed. The dissociation energy of e ϩ LiH into HPs and Li ϩ was determined to be 0.036 548 hartree.

Nonrelativistic molecular quantum mechanics without approximations: Electron affinities of LiH and LiD

“…Since their implementation basis functions ͑5͒ have been applied in several very accurate non-BO calculations of molecular systems. 15,[17][18][19] In this work we used them to determine the electron affinities of LiH and LiD.…”

Non-Born–Oppenheimer variational calculations of HT+ bound states with zero angular momentum

“…[11][12][13][14][15][16][17][18][19] The approach is based on separating the operator describing the center of mass kinetic energy from the total Hamiltonian of the system and representing the remaining internal Hamiltonian in the reference frame centered at one of the particles ͑in most cases the heaviest particle͒. In the calculation we use the explicitly correlated n-particle Gaussian functions to expand the spatial part of the wave function.…”

Non-Born–Oppenheimer calculations of the pure vibrational spectrum of HeH+

“…To achieve the best results in the parameter optimization with the least computational effort, we have recently implemented a hybrid method that combines the gradient-based optimization ͑i.e., the optimization that makes use of the analytical expressions for the gradient as opposed to the finite-difference gradient evaluation͒ with the stochastic selection method. 12,13 The strategy is based on alternating the gradient-based and the stochastic-based optimizations in growing the basis set from a small initial set generated in a gradient-based optimization to the final set. The basis set for each vibrational state of HeH + was generated in a separate calculation.…”

“…The development of such an approach and its implementation has been carried out for several years in our laboratory. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] The centerpiece of the development has been the use of various forms of the explicitly correlated Gaussian functions that are dependent on the distances between the particles ͑nuclei and electrons͒ forming the system. Recent calculations have demonstrated that, if extended Gaussian basis sets are used, very accurate results matching quite well the experimental data can be obtained.…”