The structure of e(+)LiH

The stochastic variational method (SVM) has been used to confirm the predic tion of a quantum Monte Carlo (QMC) calculation (Bressanini et al 1998 J. C hem. Phys. 109 1716) that a positron can be bound to the lithium hydride mo lecule (LiH). The adiabatic approximation was not made and the nuclear moti on was explicitly included in the calculation. A completely ab initio calcu lation gave a positron binding energy of 0.613 eV and constitutes an explic it demonstration of binding not restricted to the Born-Oppenheimer approxim ation. The fixed-core variant of the SVM was also used with a Li+ 1s(2) cor e. The positron binding energy in the fixed-core SVM was 0.909 eV, which is approximately the same as that previously reported in the QMC calculation. The mean inter-nuclear radius was 3.96 a(0) and the 2 gamma annihilation r ate of the e(+)LiH ground state was 1.64 x 10(9) s(-1).