Speaker: Benjamin Rudshteyn from Columbia University
Title: Benchmark Quantum Chemical Calculations for Transition Metal Complexes via Auxiliary Field Quantum Monte Carlo
Abstract: The accurate prediction of ionization energies is essential to understanding the electrochemistry of transition metal complexes in both materials and biological applications. However, these predictions have been hampered by the lack of gas-phase experimental data and the difficulty of applying ab initio methods due to systems containing strong dynamic and/or static electron correlation. In this work we apply all-electron phaseless auxiliary-field quantum Monte Carlo (ph-AFQMC) calculations utilizing multi-determinant trial wavefunctions and correlated sampling and compare to adiabatic (uncertainty = 1.5 kcal/mol) experiments for six metallocene complexes. We compare the results with those from density functional theory (DFT) and domain-based local pair natural orbital coupled cluster theory with single, double, and perturbative triple excitations (DLPNO-CCSD(T)). We find low mean averaged errors (MAE) for our ph-AFQMC approach using ph-AFQMC for both the correlated sampling calculation of the vertical ionization and for the population control calculation of the reorganization energy, outperforming other methods. Thus, we show that ph-AFQMC can handle realistically sized transition metal complexes with high oxidation states with the advantage of systematically improvable results. By utilizing experimental solvation energies, we compare to experimental reduction potentials.