Introduction

COMPASS (Condensed-phase Optimized Molecular Potentials for Atomistic Simulation Studies) force field represents a technology break-through in force field methods. It is the first ab initio force field that enables simultaneous and accurate prediction of condensed-phase and gas-phase properties and properties for a broad range of polymers and molecules. Consequently, this forcefield enables accurate and simultaneous prediction of structural, conformational, vibrational, and thermophysical properties for a broad range of molecules. It is also the first high-quality force field to consolidate parameters of organic and inorganic materials.

Coverage

The COMPASS forcefield has broad coverage in covalent and non-covalent molecules. Examples of the covered covalent and non-covalent systems are water and metal oxides respectively. For covalent molecular systems, this forcefield has been parameterized to predict various properties including molecular structures, vibrational frequencies, conformation energies, dipole moments, liquid structures, crystal structures, equations of state, and cohesive energy densities. For non-covalent systems, COMPASS is able to predict various solid-state properties including unit cell structures, lattice energies, elastic constants, and vibrational frequencies.
In addition to this, COMPASS supports the Morse-dispersion form that appears in some semi-ionic models, typically used in the simulation of metal oxide systems. (For atoms that are close contacts, the interaction energy is a sum of electrostatic term and a Morse-dispersion function which is a combination of a Morse and a dispersion functional form.) The contributions of the electrostatic and Morse-dispersion terms represent the ionic and covalent contributions (that are of importance in metal oxides) and the van der Waals terms represent the weak nonbonded interactions.
In addition to appropriate coverage of the molecules and structures, COMPASS is an accurate force field. In general, the procedure of parameterization of this force field consists of two phases: ab initio parameterization and empirical optimization. For organic molecules, Parameters have been derived using high-level ab initio calculations and optimized to fit experimental data of both gaseous and condensed phases. For inorganic materials, the parameterization and validations are based on energy minimization calculations. Considering the mentioned facts, this force field is appropriate for the simulations of the cementitious medium.