Born-Oppenheimer molecular dynamics and electronic properties of liquid H2S: the importance of a non-local approach to dispersion interactions

The dynamics and electronic properties of liquid H₂S were investigated by Born–Oppenheimer molecular dynamics (BOMD). The Vydrov and Van Voorhis VV10 exchange–correlation functional [J. Chem. Phys. 133 (2010) 244103] that includes non-local correlation was adopted for generating the dynamics. This functional predicts the binding energy of the (H₂S)₂ dimer in very good agreement with experiment. Emphasis was placed on the structure, polarisation effects, and electronic absorption in liquid phase. The dipole moment in liquid H₂S increases by 

$0.2$D relative to the gas phase. A very small change (

$\sim 0.1$ eV) in the position of the first maximum of the electronic absorption spectrum is observed when we compare liquid H₂S and the isolated molecule. This is in contrast to liquid water where a 

$[0.4–0.7]$ eV blue shift in the first peak of the absorption spectrum relative to the gas phase is observed. Exciton binding energies of H₂S are calculated and compared with results for water. Their importance for explaining the difference between the blue-shift in H₂S and water is discussed. The results indicate that although the (H₂S)₂ dimer is HB, some specific features characterising the structure and electronic properties of other HB liquids are not observed in liquid H₂S. The interest of a non-local treatment of van der Waals interactions in liquid H₂S is stressed.