Study of positronium hydride with a simple wavefunction: Application to the Stark effect of PsH

A compact four-parameters correlated wavefunction has been variationally optimized for the PsH system. This function exactly takes into account the whole set of cusp conditions at interparticle coalescence points. The multivariate integrations have been performed with the Wozniakowski's algorithm. The ground state energy and the two photons annihilation rate provided by this function are in good agreement with the most accurate results available in the literature. The expectation values of operators related to the position of the particles as well as the electron and positron densities have been evaluated and are discussed. The determination of the second order Stark effect energy enables to estimate the static dipole-dipole polarizability, similar to 18.3 x 10(-24) cm(3), and to study the behavior of the annihilation rate as a function of the external field strength. It decrease is correlated with the increase of the electron positron distance expectation value. (C) 1998 Elsevier Science B.V. All rights reserved.