Polarizable Water Models from Mixed Computational and Empirical Optimization

Abstract

Here we suggest a mixed computational and empirical approach serving to optimize the parameters of complex and polarizable molecular mechanics (PMM) models for complicated liquids. The computational part of the parameter optimization relies on hybrid calculations combining density functional theory (DFT) for a solute molecule with a PMM treatment of its solvent environment at well-defined thermodynamic conditions. As an application we have developed PMM models for water featuring ν = 3, 4, and 5 points of force action, a Gaussian inducible dipole and a Buckingham potential at the oxygen, the experimental liquid phase geometry, the experimental gas phase polarizability α(exp)(g) = 1.47 ų, and, for ν = 4 and 5, the gas phase value μ(exp)(g) = 1.855 D for the static dipole moment. The widths of the Gaussian dipoles and, for ν = 4 and 5, also the electrostatic geometries of these so-called TLνP models are derived from self-consistent DFT/PMM calculations, and the parameters of the Buckingham potentials (and the static TL3P dipole moment) are estimated from molecular dynamics (MD) simulations. The high quality of the resulting models is demonstrated for the observables targeted during optimization (potential energy per molecule, pressure, radial distribution functions) and a series of predicted properties (quadrupole moments, density at constant pressure, dielectric constant, diffusivity, viscosity, compressibility, heat capacity) at certain standard conditions. Remaining deficiencies and possible ways for their removal are discussed.

2D-Raman-THz spectroscopy: A sensitive test of polarizable water models

“…The TL4P model has been implemented into the home-written MD code, which has been verified against Ref. 53. The results are shown in Fig.…”

“…Tavan and co-workers have recently presented a series of polarizable water models, TLnP, 53,68,69 which feature computational simplicity together with a very accurate description of simultaneously gas-phase and liquid phase properties. Apart from a careful parametrization, the essential difference to other water models of equal complexity are Gaussian inducible dipoles.…”

Utilizing fast multipole expansions for efficient and accurate quantum-classical molecular dynamics simulations

“…Following Ref. 54, we chose the widths σ M = σ L = 0.46 Å for the inplane (M) and out-of-plane (L 1 , L 2 ) massless charges and σ H = 0.24 Å for the partial charges at the H atoms.…”

Direct computation of parameters for accurate polarizable force fields

“…For example, PFF simulations of organic or ionic liquids showed an improved correspondence of thermodynamic and structural properties with experiment, while also reproducing gas-phase dimer properties. 24,30,31,[33][34][35][36][37][38][39][40] In the field of materials science, PFFs are gaining attention as well, e.g., a polarizable Al-O potential was recently proposed that can reproduce crystal energies, lattice constants, and deformation energies of different Al x O y crystal phases. 41 Another nice example is a LiI PFF that was fitted to ab initio reference data and that reproduces properties of both the liquid and crystal phases.…”

“…Next to the relatively direct calibration of ERFF parameters with ab initio linear response data, it is also common to fit all parameters in the whole PFF to more diverse experimental and/or ab initio reference data. 22,24,37,44,[63][64][65] To avoid the empirical calibration of ERFF parameters, we will compute them exactly from the electronic wavefunc-tion obtained with an underlying variational electronic structure theory. In this approach, the ERFF is an electronic linearresponse model in which all parameters are well-defined in terms of the underlying theory.…”