Forces, stresses and related properties in solids by plane-wave auxiliary-field quantum Monte Carlo

We present accurate calculations of interatomic force and stress in solid state systems, using the plane-wave auxiliary-field quantum Monte Carlo (PW-AFQMC) method [1] . AFQMC has been shown to be an excellent many-body total energy method. Computation of observables other than the ground-state energy requires back-propagation [2], which we have implemented in the PW-AFQMC framework and to compute accurate charge densities [3]. Here we present results on computing derivatives of the total energy, including forces and stresses. Accurate AFQMC interatomic forces and stresses can be applied for a full geometry optimization in solids, which we demonstrate in the silicon beta-tin structure and molybdenum disulfide (MoS₂) monolayer. Further, we generalize the correlated-sampling technique [4] to compute observables, and demonstrate it by computing the phonon spectrum from the force fields at a low cost. This paves the way for ab initio many-body computation of thermodynamic properties.