Correlation energy of the paramagnetic electron gas at the thermodynamic limit
Physical Review B American Physical Society 107 (2023) L121105
Abstract:
The variational and diffusion quantum Monte Carlo methods are used to calculate the correlation energy of the paramagnetic three-dimensional homogeneous electron gas at intermediate to high density. Ground state energies in finite cells are determined using Slater-Jastrow-backflow trial wave functions, and finite-size errors are removed using twist-averaged boundary conditions and extrapolation of the energy per particle to the thermodynamic limit of infinite system size. Our correlation energies in the thermodynamic limit are more accurate than previous results. The present diffusion quantum Monte Carlo energies, together with our recently reported [Phys. Rev. B 105, 245135 (2022)] results at low density, are used to parameterize the correlation energy of the electron gas using a functional form that satisfies the exact asymptotic behavior at high density.Quasiparticle Effective Mass of the Three-Dimensional Fermi Liquid by Quantum Monte Carlo.
Physical review letters 127:8 (2021) 086401
Abstract:
According to Landau's Fermi liquid theory, the main properties of the quasiparticle excitations of an electron gas are embodied in the effective mass m^{*}, which determines the energy of a single quasiparticle, and the Landau interaction function, which indicates how the energy of a quasiparticle is modified by the presence of other quasiparticles. This simple paradigm underlies most of our current understanding of the physical and chemical behavior of metallic systems. The quasiparticle effective mass of the three-dimensional homogeneous electron gas has been the subject of theoretical controversy, and there is a lack of experimental data. In this Letter, we deploy diffusion Monte Carlo (DMC) methods to calculate m^{*} as a function of density for paramagnetic and ferromagnetic three-dimensional homogeneous electron gases. The DMC results indicate that m^{*} decreases when the density is reduced, especially in the ferromagnetic case. The DMC quasiparticle energy bands exclude the possibility of a reduction in the occupied bandwidth relative to that of the free-electron model at density parameter r_{s}=4, which corresponds to Na metal.GW space-time method: Energy band gap of solid hydrogen
Physical Review B American Physical Society 105:15 (2022) 155136
Abstract:
We implement the GW space-Time method at finite temperatures, in which the Green's function G and the screened Coulomb interaction W are represented in the real space on a suitable mesh and in imaginary time in terms of Chebyshev polynomials, paying particular attention to controlling systematic errors of the representation. Having validated the technique by the canonical application to silicon and germanium, we apply it to the calculation of band gaps in hexagonal solid hydrogen with the bare Green's function obtained from density functional approximation and the interaction screened within the random phase approximation. The results, obtained from the asymptotic decay of the full Green's function without resorting to analytic continuation, suggest that the solid hydrogen above 150 GPa cannot adopt an orientationally ordered hexagonal-closed-pack structure due to its metallic behavior. The demonstrated ability of the method to store the full G and W functions in memory with sufficient accuracy is crucial for its subsequent extensions to include higher orders of the diagrammatic series by means of diagrammatic Monte Carlo algorithms.Correlation energy of the spin-polarized electron liquid studied using quantum Monte Carlo simulations
Physical Review B: Condensed Matter and Materials Physics American Physical Society 108 (2023) 115134
Abstract:
Variational and diffusion quantum Monte Carlo (VMC and DMC) methods with Slater-Jastrowbackflow trial wave functions are used to study the spin-polarized three-dimensional uniform electron fluid. We report ground state VMC and DMC energies in the density range 0.5 ≤ rs ≤ 20. Finite-size errors are corrected using canonical-ensemble twist-averaged boundary conditions and extrapolation of the twist-averaged energy per particle calculated at three system sizes (N =113, 259, and 387) to the thermodynamic limit of infinite system size. The DMC energies in the thermodynamic limit are used to parameterize a local spin density approximation correlation function for inhomogeneous electron systems.Correlation energy of the spin-polarized electron liquid studied using quantum Monte Carlo simulations
Physical Review B American Physical Society (APS) 108:11 (2023) 115134