New Features of the Open Source Monte Carlo Software Brick-CFCMC: Thermodynamic Integration and Hybrid Trial Moves

Abstract

We present several new major features added to the Monte Carlo (MC) simulation code Brick-CFCMC for phase- and reaction equilibria calculations ( ). The first one is thermodynamic integration for the computation of excess chemical potentials (μ ex ). For this purpose, we implemented the computation of the ensemble average of the derivative of the potential energy with respect to the scaling factor for intermolecular interactions ( ). Efficient bookkeeping is implemented so that the quantity is updated after every MC trial move with negligible computational cost. We demonstrate the accuracy and reliability of the calculation of μ ex for sodium chloride in water. Second, we implemented hybrid MC/MD translation and rotation trial moves to increase the efficiency of sampling of the configuration space. In these trial moves, short Molecular Dynamics (MD) trajectories are performed to collectively displace or rotate all molecules in the system. These trajectories are accepted or rejected based on the total energy drift. The efficiency of these trial moves can be tuned by changing the time step and the trajectory length. The new trial moves are demonstrated using MC simulations of a viscous fluid (deep eutectic solvent).

Solubilities and Transport Properties of CO2, Oxalic Acid, and Formic Acid in Mixed Solvents Composed of Deep Eutectic Solvents, Methanol, and Propylene Carbonate

“… 67 For more details on the CFCMC method, the reader is referred elsewhere. 65 − 69 Recently, a thermodynamic integration feature has been developed in Brick-CFCMC for computing μ ex based on 64 where U is the energy of the system, and the brackets ⟨···⟩ denote an ensemble average. During CFCMC simulations, separate scaling parameters are used for intermolecular Lennard-Jones and electrostatic interactions.…”

“…The scaling parameters are continuous functions of λ and are implemented such that electrostatic interactions are not switched on before fully scaling down the Lennard-Jones interactions. For more details, including the scaling functions, the reader is referred to the work of Polat et al 64 To compute μ ex of CO 2 , oxalic acid, and formic acid in different solvents using eq 6 , the λ space was discretized into 50 bins. Separate simulations in the NPT ensemble were performed for each solute with a fixed value of λ to compute .…”

“…Subsequently, numerical integration of eq 6 was performed. More details on the thermodynamic integration feature of Brick-CFCMC can be found in the recent work of Polat et al 64 μ ex and H were computed for mixtures with 0 ≤ x DES ≤ 0.4 at 298.15 K and 1 atm and for pure reline and ethaline at 350.15 K and 1 atm.…”

“…All MC simulations were carried out with the open-source software package Brick-CFCMC, , which utilizes the Continuous Fractional Component (CFC) method , (i.e., gradual insertion/deletion of fractional molecules during the simulations). The degree of interaction between a fractional with the surrounding molecules is varied using a scaling parameter λ (0≤ λ ≤ 1), which is a degree of freedom in an expanded ensemble formulation .…”

“…The degree of interaction between a fractional with the surrounding molecules is varied using a scaling parameter λ (0≤ λ ≤ 1), which is a degree of freedom in an expanded ensemble formulation . For more details on the CFCMC method, the reader is referred elsewhere. − Recently, a thermodynamic integration feature has been developed in Brick-CFCMC for computing μ ex based on where U is the energy of the system, and the brackets ⟨···⟩ denote an ensemble average. During CFCMC simulations, separate scaling parameters are used for intermolecular Lennard-Jones and electrostatic interactions.…”