Publication date: Jul 20, 2021
Obtaining a precise theoretical description of the spectral properties of liquid water poses challenges for both molecular dynamics (MD) and electronic structure methods. The lower computational cost of the Koopmans-compliant functionals with respect to Green’s function methods allows the simulations of many MD trajectories, with a description close to the state-of-art quasi-particle self-consistent GW plus vertex corrections method (QSGW + fxc). Thus, we explore water spectral properties when different MD approaches are used, ranging from classical MD to first-principles MD, and including nuclear quantum effects. We have observed that different MD approaches lead to up to 1 eV change in the average band gap; thus, we focused on the band gap dependence with the geometrical properties of a system to explain such spread. We have evaluated the changes in the band gap due to variations in the intramolecular O–H bond distance and HOH angle, as well as the intermolecular hydrogen bond O···O distance and the OHO angles. We have observed that the dominant contribution comes from the O–H bond length; the O···O distance plays a secondary role, and the other geometrical properties do not significantly influence the gap. Furthermore, we analyze the electronic density of states (DOS), where the KIPZ functional shows good agreement with the DOS obtained with state-of-art approaches employing quasi-particle self-consistent GW plus vertex corrections. The O–H bond length also significantly influences the DOS. When nuclear quantum effects are considered, broadening of the peaks driven by the broader distribution of the O–H bond lengths is observed, leading to a closer agreement with the experimental photoemission spectra.
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|1.3 KiB||Description of each file|
|32.1 KiB||Snapshot used for rescaling the O-H bond lengths of water molecules, being the 11th step the non-rescaled one, 1 to 10 with lower O-H bond lengths, and 12 to 21 with longer O-H bond lengths. Cubic box of side 9.8667 Angstroms.|
|56.4 KiB||20 snapshots collected from a classical molecular dynamics with 64 water molecules, using the SPCE-FH force field. Simulation at 300 K with a cubic box with a side of 12.415 Angstroms. Simulation at 300 K with a cubic box with a side of 12.415 Angstroms.|
|10.9 MiB||20 snapshots collected from a classical molecular dynamics with 64 water molecules, using the TIP4P force field. Simulation at 300 K with a cubic box with a side of 12.415 Angstroms.|