Ab initio molecular dynamics of liquid water using embedded-fragment second-order many-body perturbation theory towards its accurate property prediction

Abstract

A direct, simultaneous calculation of properties of a liquid using an ab initio electron-correlated theory has long been unthinkable. Here we present structural, dynamical, and response properties of liquid water calculated by ab initio molecular dynamics using the embedded-fragment spin-component-scaled second-order many-body perturbation method with the aug-cc-pVDZ basis set. This level of theory is chosen as it accurately and inexpensively reproduces the water dimer potential energy surface from the coupled-cluster singles, doubles, and noniterative triples with the aug-cc-pVQZ basis set, which is nearly exact. The calculated radial distribution function, self-diffusion coefficient, coordinate number, and dipole moment, as well as the infrared and Raman spectra are in excellent agreement with experimental results. The shapes and widths of the OH stretching bands in the infrared and Raman spectra and their isotropic-anisotropic Raman noncoincidence, which reflect the diverse local hydrogen-bond environment, are also reproduced computationally. The simulation also reveals intriguing dynamic features of the environment, which are difficult to probe experimentally, such as a surprisingly large fluctuation in the coordination number and the detailed mechanism by which the hydrogen donating water molecules move across the first and second shells, thereby causing this fluctuation.

Absolute proton hydration free energy, surface potential of water, and redox potential of the hydrogen electrode from first principles: QM/MM MD free-energy simulations of sodium and potassium hydration

“…Although the MP2 level of theory is only the first scheme in a hierarchy of approaches to account for electron-correlation effects, 179 it has been shown to provide a good compromise between accuracy and computational effort in the context of ion-water interactions. 66,67,77,78,130,155,180,181 Recent simulations of the bulk water dynamics at this level of theory [123][124][125][126][127] also suggest that it is adequate for the representation of the liquid properties.…”

“…The QM/MM MD simulations rely on the quantum-mechanical charge field (QMCF) approach, 158,159 which belongs to the family of adaptive QM/MM methods 148,149,160 and has been applied with success in the past to investigations of solvated ions, 153,154 molecules, 161,162 coordination complexes, 163,164 and biomolecular systems. 165,166 Single-determinantal approaches such as ab initio HartreeFock 167,168 (HF) or DFT 169,170 have a limited accuracy/reliability 120,[123][124][125][126][127]155,[171][172][173][174][175][176] in the description of hydration phenomena. Thus, a correlated ab initio method is employed here to describe the QM subsystem (ion and first hydration shell), namely, resolution-of-identity secondorder Møller-Plesset perturbation 177,178 (RIMP2).…”

“…For the cluster-continuum calculations, error sources include the selection of the clusters (sampling), their small sizes (smooth trends and fast convergence being required for a meaningful extrapolation 117 ), the estimation of the cluster entropy, 118-120 the choice of a cluster permittivity in the CE calculation, and the problems associated with a QM-CE boundary (surface definition, atomic radii). For the CPMD/BOMD calculations, error sources include the shortcomings of DFT methods in terms of electron correlation (including dispersion), affecting both bulk water properties [121][122][123][124][125][126][127][128][129][130] and ion-water interactions, 66,67,105,131 the small system sizes considered (resulting in a high weight for the approximate finite-size correction term), the very limited sampling times, the ambiguity in defining the appropriate reference potential within DFT water, 21,112,[132][133][134][135][136] and the numerical problems (see, e.g., footnotes 42 and 45 in Ref. 111) associated with creating a species or injecting electrons when applying computational alchemy in a QM framework [137][138][139][140][141][142][143] (see, however, Refs.…”

Communication: Librational dynamics in water, sI and sII clathrate hydrates, and ice Ih: Molecular-dynamics insights

“…17 MD, with various potentials, has probed vibrational density of states (DOS) of liquid water, 18 ice, 19 and hydrates. [20][21][22][23][24][25][26][27] More recently, liquid-water MP2-based MD has offered prospects of better agreement with INS-DOS, 28 whilst Density Functional Theory (DFT)-MD has shown qualitative DOS agreement. 25 DFT calculations on ice Ih have also shown reasonably good DOS agreement with INS.…”

Enhancing performance of ionic liquid property prediction with molecular dynamics.

“…These more expensive calculations tend to be more accurate for liquid structures, because the liquid is more comparable to the solid than to the gas (in vacuo). Previous ab initio studies of solid crystals indicate that multiplying the charges by a factor of 0.7-0.9 14 can create force fields with appropriate electrostatic interactions that reproduce dynamic properties of ILs well. By using MD rather than ab initio methods, IL properties can be predicted on a large-scale through molecular simulation.…”