High pressure ionic and molecular crystals of ammonia monohydrate within density functional theory

A combination of first-principles density functional theory calculations and a search over structures predicts the stability of a proton-transfer modification of ammonia monohydrate with space group P4/nmm. The phase diagram is calculated with the PBE density functional, and the effects of a semi-empirical dispersion correction, zero point motion, and finite temperature are investigated. Comparison with MP2 and coupled cluster calculations shows that the PBE functional over-stabilizes proton transfer phases because too much electronic charge moves with the proton. This over-binding is partially corrected by using the PBE0 hybrid exchange-correlation functional, which increases the enthalpy of P4/nmm by about 0.6 eV per formula unit relative to phase I of ammonia monohydrate (AMH-I) and shifts the transition to the proton transfer phase from the PBE pressure of 2.8 GPa to about 10 GPa. This is consistent with experiment as proton transfer phases have not been observed at pressures up to ~9 GPa, while higher pressures have not yet been explored experimentally.Comment: 10 pages, 9 figure

From dimers to the solid-state: Distributed intermolecular force-fields for pyridine

A.A. thanks A.W.E. financial support through the EngDoc studentship from M3S Centre for Doctoral Training (EPSRC Grant No. EP/G036675/1). General computational infrastructure used is developed under No. EPSRC EP/K039229/1

Simulation study of pressure and temperature dependence of the negative thermal expansion in Zn(CN)(2)

12 pages, 16 figures12 pages, 16 figures12 pages, 16 figures12 pages, 16 figure

Charge Transfer from Regularized Symmetry-Adapted Perturbation Theory

16 pages, 16 figure

Beyond Born-Mayer: Improved Models for Short-Range Repulsion in ab Initio Force Fields

Short-range repulsion within intermolecular force fields is conventionally described by either Lennard-Jones (<i>A</i>/<i>r</i>¹²) or Born–Mayer (<i>A</i> exp­(−<i>Br</i>)) forms. Despite their widespread use, these simple functional forms are often unable to describe the interaction energy accurately over a broad range of intermolecular distances, thus creating challenges in the development of ab initio force fields and potentially leading to decreased accuracy and transferability. Herein, we derive a novel short-range functional form based on a simple Slater-like model of overlapping atomic densities and an iterated stockholder atom (ISA) partitioning of the molecular electron density. We demonstrate that this Slater–ISA methodology yields a more accurate, transferable, and robust description of the short-range interactions at minimal additional computational cost compared to standard Lennard-Jones or Born–Mayer approaches. Finally, we show how this methodology can be adapted to yield the standard Born–Mayer functional form while still retaining many of the advantages of the Slater-ISA approach

Anomalous nonadditive dispersion interactions in systems of three one-dimensional wires

10 pages, 8 figures, 1 tableFinancial support was provided by the U. K. Engineering and Physical Sciences Research Council (EPSRC). Part of the computations have been performed using the K computer at Advanced Institute for Computational Science, RIKEN. R.M. is grateful for financial support from KAKENHI Grants No. 23104714, No. 22104011, and No. 25600156, and from the Tokuyama Science Foundation