arXiv subjects
Publications and source records attributed to Ethan A. Vo.
Over the past decade, the Python-based Simulations of Chemistry Framework (PySCF) has developed into a widely used open-source platform for electronic structure theory and quantum chemical method development. This article reviews the major advances since the previous overview in 2020, covering new modules and methodology, infrastructure changes, and performance benchmarks.
For ethylene carbonate on the (100) surface of lithium, we calculate the adsorption energy in two binding motifs as well as the barrier height for a ring-opening decomposition reaction. We validate a scheme for producing results in the thermodynamic limit by correcting results obtained on finite lithium clusters containing only 40-100 atoms, which enables the use of hybrid density functionals, the random-phase approximation, and correlated wavefunction theories such as coupled-cluster theory and auxiliary-field quantum Monte Carlo. We find that the high-level theories agree to within 2-5 kcal/mol and can therefore serve as benchmarks for more affordable methods. Using our reference data, we demonstrate that generalized gradient approximation functionals, such as PBE, are not sufficiently accurate for reaction barrier heights, and we identify $ω$B97X-V as an especially promising functional for the interfacial chemistry of electrolyte solvents at lithium metal anodes.
We report the core binding energies of K-edge and L-edge transitions in simple semiconducting and insulating solids using periodic equation-of-motion coupled-cluster theory with single and double excitations (EOM-CCSD). In our all-electron calculations, we use triple zeta basis sets with core correlation, and we sample the Brillouin zone using up to 4x4x4 k-points. Our final numbers, which are obtained through composite corrections and extrapolation to the thermodynamic limit, exhibit errors of about 2 eV when compared to experimental values. This level of accuracy from CCSD is about the same as it is for molecules. A low-scaling approximation to EOM-CCSD performs marginally worse at lower cost, with errors of about 3 eV.
We calculate the band gaps of 12 inorganic semiconductors and insulators composed of atoms from the first three rows of the periodic table using periodic equation-of-motion coupled-cluster theory with single and double excitations (EOM-CCSD). Our calculations are performed with atom-centered triple-zeta basis sets and up to 64 $k$-points in the Brillouin zone. We analyze the convergence behavior with respect to number of orbitals and number of $k$-points sampled, using composite corrections and extrapolations to produce our final values. When accounting for electron-phonon corrections to experimental band gaps, we find that EOM-CCSD has a mean signed error of $-0.12$ eV and a mean absolute error of $0.42$ eV; the largest outliers are C (error of $-0.93$ eV), BP ($-1.00$ eV), and LiH ($+0.78$ eV). Surprisingly, we find that the more affordable partitioned EOM-MP2 theory performs as well as EOM-CCSD.