First-Principles Calculations of Optical Spectra in Liquid Water using GW plus Bethe-Salpeter Equation approach

Optical spectroscopy is a powerful experimental technique to probe the electronic structure of liquid water. An accurate modeling of optical spectra demands accurate descriptions of both molecular structures and electron-hole excitation processes from first principles. We simulate the water structure from deep potential path-integral molecular dynamics simulations, where the neural network potential is trained on the state-of-the-art density-functional theory data with the SCAN0 hybrid functional. Using the equilibrated liquid structure, we compute optical spectra of liquid water by solving the GW-Bethe-Salpeter equation as implemented in the BerkeleyGW software package. Our theoretical optical spectrum agrees well with existing experiments. We further analyze the effects from quantum nuclei and thermal fluctuations on the optical spectrum.