Compton Profile of Solid and Liquid Lithium from Quantum Monte Carlo

Compton scattering cross section is directly related to the electronic momentum distribution and provides an important check of many-body theory. We computed the Compton profile of solid and liquid lithium using quantum Monte Carlo (QMC) and compared with recent experiments obtaining excellent agreement. Importantly, we find it necessary to explicitly include the core electrons for quantitative accuracy. To account for lattice effects, we sampled finite-temperature configurations using molecular dynamics (MD), then performed pseudopotential diffusion Monte Carlo (DMC) simulations on each configuration. We used Slater-Jastrow wavefunction and twist-averaged boundary condition. QMC pseudopotential correction was derived from an all-electron DMC simulation of the perfect crystal. Our calculations provide the first all-electron QMC benchmark for the Compton profile of lithium under both liquid and solid conditions.