On reverse Monte Carlo constraints and model reproduction

Abstract

Reverse Monte Carlo (RMC) simulations were performed to investigate the effectiveness of any combination of five experimentally motivated constraints on the reproduction of a test case, a ternary ab initio model. It was found that low energy structures fitting a variety of constraints commonly used in the RMC methodology could still provide an incorrect description of the chemical structural unit populations in multi-elemental systems. It is shown that the use of an elemental bond type constraint is an effective way to avoid this. © 2017 Wiley Periodicals, Inc.

Large and realistic models of amorphous silicon

“…have proposed use of a constraint for removal of these highly constrained 3 membered rings in several of their works. 16,33 FEAR method which incorporates accurate ab initio interaction enables us to remove these high energy structures without satisfying an extra criterion.…”

“…The difficulty associated with the inversion of diffraction data using RMC simulations has led to the development of a number of hybrid approaches in the past decade. 16,17 Hybrid approaches retain the spirit of the RMC philosophy as far as the use of experimental data in simulations is concerned but go beyond RMC by using an extended penalty function, which involves total energy and forces from appropriate classical/quantummechanical force fields, in addition to few structural or geometrical constraints. The experimentally constrained molecular relaxation 18,19 (ECMR), the first-principle assisted structural solutions 20 (FPASS), and the recently developed forceenhanced atomic relaxation [21][22][23][24] (FEAR) are a few examples of hybrid approaches, which have successfully incorporated experimental information in atomistic simulations to determine structures consistent with both theory and experiments.…”

Evolution of amorphous carbon across densities: An inferential study

“…Often these models result in highly-constrained or under-constrained structures, which may turn out be inaccurate or totally unrealistic. [9,10] To resolve these in-adequacies different experimentally motivated con-straints have been proposed such as: multiple scattering data [11][12][13], bond-angle constraints [14], coordination constraints [6] and so on, which can be quite effective. [9] The real concern about constraints is that they introduce bias into the modeling scheme.…”

“…[9,10] To resolve these in-adequacies different experimentally motivated con-straints have been proposed such as: multiple scattering data [11][12][13], bond-angle constraints [14], coordination constraints [6] and so on, which can be quite effective. [9] The real concern about constraints is that they introduce bias into the modeling scheme. Alternatively, energy functional based constraints involve minimization of total energy and total forces.…”

Detection of Ring and Adatom Defects in Activated Disordered Carbon via Fluctuation Nanobeam Electron Diffraction

“…For example, similar fitting of fluctuation electron microscopy data has provided insights to support the long contended existence of paracrystals in amorphous silicon [23], although the modelling of four-body correlations and medium range order is computationally intensive. Computationally efficient bond angle constraints for nearest neighbours [40] have been demonstrated to be particularly effective for statistically reconstituting the structure of abinitio models of glass in a recent reverse Monte Carlo benchmark study [41]. Hence we expect that the experimentally accessible angular correlations in the PADF can be readily exploited to efficiently refine the short range order for a variety of disordered solids.…”