Development of an AMOEBA water model using GEM distributed multipoles

Abstract

Distributed multipoles obtained from the Gaussian electrostatic model (GEM) have been previously shown to be amenable for use in the AMOEBA force field [JCTC(2012) 12, 5072]. GEM distributed multipoles (GEM-DM) were determined for several systems including water. This previous AMOEBA water model with GEM-DM included only monopoles on the hydrogens and multipoles up to quadrupoles on the oxygen. This model showed good agreement with experiment for several properties at room temperature, but not at higher temperatures. In this contribution, we present the development of an AMOEBA water model using GEM-DM with distributed multipoles for each atomic site up to the quadrupole level. Quantum mechanical energy decomposition analysis has been employed to compare each term of the force field for parametrization. The inclusion of higher-order multipoles on hydrogen atoms is shown to provide better agreement with experiment on a number of properties including liquid density ( $$\rho$$ ), enthalpy of vaporization ( $$\Delta H_\mathrm{vap}$$ ), heat capacity ( $$C_{p}$$ ), and self-diffusion coefficient (D) for a range of temperatures.