Atomistic potential for graphene and other sp²carbon systems

Abstract

We introduce a torsional force field for sp carbon to augment an in-plane atomistic potential of a previous work [G. Kalosakas et al., J. Appl. Phys., 2013, 113, 134307] so that it is applicable to out-of-plane deformations of graphene and related carbon materials. The introduced force field is fit to reproduce density-functional-theory calculation data of appropriately chosen structures. The aim is to create a force field that is as simple as possible so it can be efficient for large scale atomistic simulations of various sp carbon structures without significant loss of accuracy. We show that the complete proposed potential reproduces characteristic properties of fullerenes and carbon nanotubes. In addition, it reproduces very accurately the out-of-plane acoustic and optical modes of graphene's phonon dispersion as well as all phonons with frequencies up to 1000 cm.

Molecular Dynamics of CH4/N2 Mixtures on a Flexible Graphene Layer: Adsorption and Selectivity Case Study

“…Moreover, since graphene is, in fact, flexible, it is then clear that in order to safely disregard its internal movements an atomistic model is definitely required, the simplified united-atom model being absolutely inadequate. On the other hand, if the flexibility of graphene is explicitly accounted for by means of the appropriate force field -the field 2 m (Fthenakis et al, 2017) conceptually being the one of choice-, both atomistic and united-atom models provide very similar results.…”

“…Observe that this field 2 m should be considered as the most adequate of the three as it has been specifically developed for graphene and includes the full set of parameters needed to describe the intramolecular motions of the sheet. In fact, it reproduces very accurately the out-of-plane acoustic and optical modes of graphene's phonon dispersion as well as all phonons with frequencies up to 1,000 cm −1 (Fthenakis et al, 2017). Anyway, at least in what adsorption concerns, the differences in the results from the three fields are certainly very small, as shown below.…”

“…This field, denoted field 2 from now on, only takes into account stretching terms and bending terms. However, later on, the same authors extended the field with a torsional term and this constitutes the third field, referred to as field 2 m (field 2 modified) from now on in this work (Fthenakis et al, 2017)…”

“…In this work, we follow up on these previous works with a classical molecular dynamics study of the methane/nitrogen gas mixture in order to assess the influence of flexibility on the separation of both gases. In a similar way as in these previous works, we will use three intramolecular force fields —including stretch, bending and torsional terms—found in the literature that we have implemented and compare their performance to the typically modeled rigid sheet fixed in the simulation box (Walther et al, 2001; Kalosakas et al, 2013; Fthenakis et al, 2017).…”

The COMPASS force field: Validation for carbon nanoribbons

“…It is assumed that the force field parameters should repro- * asavin@center.chph.ras.ru † mikhail.mazo1@gmail.com duce the value of mechanical moduli and vibration spectrum of nanoparticles, but the standard parameter sets of the abovementioned force fields have been received taking into account only in-plane frequency spectrum or/and in-plane molecular mechanics. Taking into account out-of-plane vibrations made it possible to significantly improve the matching of the bending rigidity modulus and dispersion curves calculated in MD with the available experimental data and QM simulation for force fields Morse [36,37], MEAM [38] and DREIDING [39].…”