Quantum Monte Carlo Pair Orbital Wave Functions for Periodic Systems

We derive many-body single and multireference wave functions for quantum Monte Carlo of periodic systems with an antisymmetric portion that explicitly integrates over the Brillouin zone of one-particle Bloch states. The wave functions are BCS-like determinants for singlets and Pfaffians for polarized states built with appropriate pair orbitals. This ab initio formalism is broadly applicable, e.g., to description of quasiparticle band gaps and optical excitations and to systems with complicated Fermi surfaces. It generalizes to spin-dependent interactions using two-component spinor pairs.