Accurate theoretical spectroscopy of few-electron systems

Faculty Development Competitive Research Grant Program 2021-2023

This proposed project will focus on the development of methods for calculations of atoms, small molecules, and complexes, that are currently out of reach for the explicitly correlated variational methods. We will employ new types of partially correlated Gaussian (PCG) basis functions that will allow us to extend the applicability of accurate atomic theory to atoms and ions with 10 or more electrons. These new methods will also be used in calculations of small molecules, in particular tri- and poly-atomic molecules without assuming the Born–Oppenheimer approximation. The currently existing approaches that are available for calculations of small atoms and molecules are very powerful [19, 20, 34], yet difficult to scale to larger systems. At the same time we will aim to preserve all the unique features of the ECG methods, in particular the ability to evaluate all matrix elements analytically (at least in principle) for an arbitrary number of particles, fast convergence, and high accuracy. The ultimate goal of this effort is to elevate the predictive ability of the molecular quantum mechanics to a new level. The developed methods will be implemented in a software package and we will use it in various applications pertinent to spectroscopy of few-electron systems. We believe our developments will also have great value for testing and benchmarking more traditional quantum-chemical approaches ranging from CI (configuration interaction), coupled cluster (CC), Quantum Monte-Carlo (QMC) and density-functional theory (DFT) that are routinely used in the molecular science.