Benchmarking of Molecular Dynamics Force Fields for Solid–Liquid and Solid–Solid Phase Transitions in Alkanes

Abstract

Accurate prediction of alkane phase transitions involving solids is needed to prevent catastrophic pipeline blockages, improve lubrication formulations, smart insulation, and energy storage, as well as bring fundamental understanding to processes such as artificial morphogenesis. However, simulation of these transitions is challenging and therefore often omitted in force field development. Here, we perform a series of benchmarks on seven representative molecular dynamics models (TraPPE, PYS, CHARMM36, L-OPLS, COMPASS, Williams, and the newly optimized Williams 7B), comparing with experimental data for liquid properties, liquid–solid, and solid–solid phase transitions of two prototypical alkanes, n-pentadecane (C15) and n-hexadecane (C16). We find that existing models overestimate the melting points by up to 34 K, with PYS and Williams 7B yielding the most accurate results deviating only 2 and 3 K from the experiment. We specially design order parameters to identify crystal–rotator phase transitions in alkanes. United-atom models could only produce a rotator phase with complete rotational disorder, whereas all-atom models using a 12-6 Lennard-Jones potential show no rotator phase even when superheated above the melting point. In contrast, Williams (Buckingham potential) and COMPASS (9-6 Lennard-Jones) reproduce the crystal-to-rotator phase transition, with the optimized Williams 7B model having the most accurate crystal–rotator transition temperature of C15.

Synthesis of N-doped carbon quantum dots as lubricant additive to enhance the tribological behavior of MoS2 nanofluid

“…These nanoparticles were placed between two iron slabs, and the dimension of the models was 114 Å × 40 Å × 90 Å. The interatomic interactions between metal atoms were modified by the embedded atom method (EAM) potential [32], and meanwhile, the van der Waals interactions between atoms were modified using the 12-6 Lennard-Jones potential [33].…”

Molecular Dynamics Simulation of the Crystallization Behavior of Octadecane on a Homogeneous Nucleus

“…The unit cell angle α is 12% smaller than the literature value, β 9% and γ 1% smaller. At the end of the represented study, further works were published also reporting good results for the simulation of the crystal structure of alkanes with different force fields [24][25][26]. The united-atom TraPPE seems promising with some limitations in representing the crystals and phase change.…”

On the colossal barocaloric effect in higher n-alkanes

“…Both FFs have been validated and widely used in MD studies of linear hydrocarbons, showing good agreement for prediction of PvT behavior and other relevant thermodynamic and transport properties of liquid and solid phases. [36][37][38][39][40] Simulation boxes for alkane melts modeled by using PYS 35,36 were created by randomly placing 1500 or 1000 chains (see Table S4 in the ESI †) using the PACKMOL 41 package. Initial conguration les were obtained by using the Chemstruct (available at github.com/pdemingos/chemstruct) Python package.…”