Ab initio statistical mechanics of surface adsorption and desorption. II. Nuclear quantum effects

Abstract

We show how the path-integral formulation of quantum statistical mechanics can be used to construct practical ab initio techniques for computing the chemical potential of molecules adsorbed on surfaces, with full inclusion of quantum nuclear effects. The techniques we describe are based on the computation of the potential of mean force on a chosen molecule, and generalise the techniques developed recently for classical nuclei. We present practical calculations based on density functional theory with a generalised-gradient exchange-correlation functional for the case of H 2 O on the MgO (001) surface at low coverage. We note that the very high vibrational frequencies of the H 2 O molecule would normally require very large numbers of time slices (beads) in path-integral calculations, but we show that this requirement can be dramatically reduced by employing the idea of thermodynamic integration with respect to the number of beads. The validity and correctness of our path-integral calculations on the H 2 O/MgO (001) system are demonstrated by supporting calculations on a set of simple model systems for which quantum contributions to the free energy are known exactly from analytic arguments.

Calculating the Entropy Loss on Adsorption of Organic Molecules at Insulating Surfaces

“…33 ), detailed studies started to appear more recently in the context of molecular association in solutions, 34 molecular adsorption from solutions, 35 formation of ordered monolayers at surfaces, 15 and understanding temperature programmed desorption (TPD) experiments. 36 The experimentally measured enthalpies and entropies of adsorption of relatively small molecules on oxide surfaces have been summarized in ref. 37 However, detailed studies of the adsorption of large organic molecules at insulating surfaces are still challenging and often confined to static simulations.…”

Path-integral simulation of solids

“…Alfe and Gillan have recently employed path-integral simulations in combination with ab initio DFT calculations to construct practical techniques for computing the chemical potential of molecules adsorbed on surfaces, with full inclusion of nuclear quantum effects 247 . These authors presented practical calculations for the case of H 2 O on the MgO (001) surface at low coverage.…”

Inverse Temperature Dependence of Nuclear Quantum Effects in DNA Base Pairs

“…19,22,24,25 Indeed this concept has proved to be useful in explaining a host of phenomena in e.g. liquid water, ice and biomolecules [25][26][27][28][29][30][31] and has seen recent experimental verification. 32 Nonetheless, most work to date has focused on geometrical properties and direct information on how and to what extent NQEs influence the strengths of HBs 33 is desirable.…”