Electronic properties of liquid ammonia: A sequential molecular dynamics/quantum mechanics approach

Abstract

The electronic properties of liquid ammonia are investigated by a sequential molecular dynamics/quantum mechanics approach. Quantum mechanics calculations for the liquid phase are based on a reparametrized hybrid exchange-correlation functional that reproduces the electronic properties of ammonia clusters [(NH3)n; n=1–5]. For these small clusters, electron binding energies based on Green’s function or electron propagator theory, coupled cluster with single, double, and perturbative triple excitations, and density functional theory (DFT) are compared. Reparametrized DFT results for the dipole moment, electron binding energies, and electronic density of states of liquid ammonia are reported. The calculated average dipole moment of liquid ammonia (2.05±0.09D) corresponds to an increase of 27% compared to the gas phase value and it is 0.23D above a prediction based on a polarizable model of liquid ammonia [Deng et al., J. Chem. Phys. 100, 7590 (1994)]. Our estimate for the ionization potential of liquid ammonia is 9.74±0.73eV, which is approximately 1.0eV below the gas phase value for the isolated molecule. The theoretical vertical electron affinity of liquid ammonia is predicted as 0.16±0.22eV, in good agreement with the experimental result for the location of the bottom of the conduction band (−V0=0.2eV). Vertical ionization potentials and electron affinities correlate with the total dipole moment of ammonia aggregates.