Coupled cluster benchmarks of water monomers and dimers extracted from density-functional theory liquid water: The importance of monomer deformations

Abstract

To understand the performance of popular density-functional theory exchange-correlation (xc) functionals in simulations of liquid water, water monomers and dimers were extracted from a PBE simulation of liquid water and examined with coupled cluster with single and double excitations plus a perturbative correction for connected triples [CCSD(T)]. CCSD(T) reveals that most of the dimers are unbound compared to two gas phase equilibrium water monomers, largely because monomers within the liquid have distorted geometries. Of the three xc functionals tested, PBE and BLYP tend to predict too large dissociation energies between monomers within the dimers. We show that this is because the cost to distort the monomers to the geometries they adopt in the liquid is systematically underestimated with these functionals. PBE0 reproduces the CCSD(T) monomer deformation energies very well and consequently the dimer dissociation energies much more accurately than PBE and BLYP. Although this study is limited to water monomers and dimers, the results reported here may provide an explanation for the overstructured radial distribution functions routinely observed in BLYP and PBE simulations of liquid water and are of relevance to water in other phases and to other associated molecular liquids.

Nature of proton transport in a water-filled carbon nanotube and in liquid water

“…32 replicas per nucleus in association with normal-mode coordinates were used in PIMD to represent the imaginary time path-integral at 300 K, a temperature controlled by a Nosé-Hoover chain thermostat. 48 In light of the well-known over-structuring of liquid water with PBE, [49][50][51] test calculations were also performed at 330 K but no significant differences in the PT mechanism compared to the 300 K simulations were found. Additional computational details and convergence tests are reported in the supporting materials.…”

The individual and collective effects of exact exchange and dispersion interactions on the ab initio structure of liquid water

“…[43][44][45][46]62 In comparison to GGAs, these studies demonstrated that the energetic, structural, and vibrational properties of these systems, as predicted by hybrid DFT calculations, are generally in closer agreement with the available experimental data. [43][44][45][46][59][60][61][62] Although applications of hybrid functionals to liquid water have been relatively rare in the literature, it was found that PBE0 63,64 greatly improves upon the accuracy of the vibrational spectrum of liquid water. 29,35 In the same breath, however, ambiguities exist and still remain concerning the effects of Exx on the structure of liquid water; while some studies have inferred a softening of the structure with hybrid functionals over GGAs, 23,29,35 others have found the effects of Exx to be negligible in this regard.…”

Local structure analysis in ab initio liquid water

“…In the microscopic structure of water, this complexity arises due to a subtle balance between directional hydrogenbonded interactions and weaker van der Waals (vdW) interactions which are non-directional [1][2][3][4][5][6][7] . In fact, this set of intricate intermolecular interactions gives rise to many of the non-trivial thermodynamic and kinetic behaviors observed in water, particularly in the liquid phase, which significantly differs from many other simple liquids in properties such as the isothermal compressibility, heat capacity, and thermal expansivity, which all seem to diverge at low temperature [8][9][10] .…”