Many-body calculations for the relaxed (110) surface of GaAs

Quantum Monte Carlo methods are a stochastic approach to directly tackle th e many-body problem in solids. They have proven to describe virtually exact ly the ground state of correlated bulk systems, like the homogeneous electr on gas or solids of C, Ge, Si and GaAs. Especially Variational quantum Mont e Carlo calculations using nonlocal abinitio pseudopotentials offer a way t o study systematically many-body effects at solid surfaces, safely founded on the variational principle "the lower the energy, the better the wave fun ction". Here we report on first attempts for the relaxed (110) surface of G aAs, serving as a prototype of semiconductor surfaces. A finite layer geome try is chosen as the boundary condition of the multidimensional stochastic integration scheme. The exact many-body Hamiltonian is cast in a form allow ing for rapid evaluation. New parameters in the correlated trial wave funct ion increase the variational freedom necessary to take into account the inf luence of the surface. Their physical meaning and their statistical signifi cance are discussed in detail.