[Show abstract][Hide abstract] ABSTRACT: We show how accurate benchmark values of the surface formation energy of crystalline lithium hydride can be computed by the complementary techniques of quantum Monte Carlo (QMC) and wavefunction-based molecular quantum chemistry. To demonstrate the high accuracy of the QMC techniques, we present a detailed study of the energetics of the bulk LiH crystal, using both pseudopotential and all-electron approaches. We show that the equilibrium lattice parameter agrees with experiment to within 0.03 %, which is around the experimental uncertainty, and the cohesive energy agrees to within around 10 meV per formula unit. QMC in periodic slab geometry is used to compute the formation energy of the LiH (001) surface, and we show that the value can be accurately converged with respect to slab thickness and other technical parameters. The quantum chemistry calculations build on the recently developed hierarchical scheme for computing the correlation energy of a crystal to high precision. We show that the hierarchical scheme allows the accurate calculation of the surface formation energy, and we present results that are well converged with respect to basis set and with respect to the level of correlation treatment. The QMC and hierarchical results for the surface formation energy agree to within about 1 %. Comment: 16 pages, 4 figures
[Show abstract][Hide abstract] ABSTRACT: We present a critical comparison of the incremental and hierarchical methods for the evaluation of the static cohesive energy of crystalline neon. Both of these schemes make it possible to apply the methods of molecular electronic structure theory to crystalline solids, offering a systematically improvable alternative to density functional theory. Results from both methods are compared with previous theoretical and experimental studies of solid neon and potential sources of error are discussed. We explore the similarities of the two methods and demonstrate how they may be used in tandem to study crystalline solids.
[Show abstract][Hide abstract] ABSTRACT: The lattice parameter, bulk modulus, and cohesive energy of lithium hydride are calculated to very high accuracy through a combination of periodic and finite-cluster electronic structure calculations. The Hartree-Fock contributions are taken from earlier work in which plane-wave calculations were corrected for pseudopotential errors. Molecular electronic structure calculations on finite clusters are then used to compute the correlation contributions and finite-size effects are removed through the hierarchical scheme. The systematic improvability of the molecular electronic structure methods makes it possible to converge the static cohesive energy to within a few tenths of a millihartree. Zero-point energy contributions are determined from density functional theory phonon frequencies. All calculated properties of lithium hydride and deuteride agree with empirical observations to within experimental uncertainty.