Comparison of density-functional, tight-binding, and empirical methods for the simulation of amorphous carbon

Abstract

Amorphous carbon networks are used to test various levels of theoretical approaches to molecular dynamics simulations. The density-functional theory as implemented in the Car-Parrinello method, nonorthogonal tightbinding method, the environment-dependent interaction potential ͑EDIP͒, and the Brenner potential are compared directly in liquid quench simulations containing 125 atoms at four densities. We find that at low densities the predictions of the Brenner potential are in agreement with those from density-functional theory, while structures produced by nonorthogonal tight-binding method compare well with density-functional theory at all densities. The tight-binding method does, however, find a slightly lower sp 3 fraction at high densities and the presence of singly coordinated atoms at low densities. The frequency of three-membered rings are underpredicted by the tight-binding and EDIP methods due to an overestimate of strain energy relative to densityfunctional theory and experiment. Aside from the small rings, and a slight underestimate in sp 3 fraction at the highest densities, the EDIP simulations are in very good agreement with density-functional theory. The EDIP method is also used to quantify the statistical variability of liquid quenching, and comparisons with film growth simulations verify that liquid quenching is a good representation of bulk amorphous carbon.

Modeling the Phase Diagram of Carbon

“…At even lower temperatures this feature becomes more and more evident, but for temperatures lower than ~4500 K the liquid freezes into a mainly four fold coordinated amorphous structure. This observation is consistent with quenching MD simulations [29,30] to ob tain the tetrahedral amorphous carbon. In those simulations a mainly threefold liquid freezes into an almost completely fourfold amorphous.…”

Milestones in molecular dynamics simulations of single-walled carbon nanotube formation: A brief critical review

“…Besides these grave deÀ ciencies, the standard REBO potential has À several other well-known problems. For example, in modeling gas-phase carbon densities it overestimates the sp 3 fraction compared to corresponding DFT simulations [40], while it underestimates the sp fraction [41] which is of paramount importance with respect to fullerene cage self-assembly [42]. Consequently, task 1a is never addressed in REBO-type MD simulations.…”

Effect of microstructure on the thermal conductivity of disordered carbon

“…2) exhibits no such variability, finding little deviation from a straight line fitted through the simulation data points. This ability to eliminate uncertainty and identify functional relationships is a strength of the computational approach, and reminiscent of earlier work in which a linear relationship between sp 3 fraction and density was demonstrated via simulation [23].…”