Abstract
Fitted interatomic potentials are widely used in atomistic simulations thanks to their ability to compute the energy and forces on atoms quickly. However, the simulation results crucially depend on the quality of the potential being used. Force matching is a method aimed at constructing reliable and transferable interatomic potentials by matching the forces computed by the potential as closely as possible, with those obtained from first principles calculations. The potfit program is an implementation of the force-matching method that optimizes the potential parameters using a global minimization algorithm followed by a local minimization polish. We extended potfit in two ways. First, we adapted the code to be compliant with the KIM Application Programming Interface (API) standard (part of the Knowledgebase of Interatomic Models project). This makes it possible to use potfit to fit many KIM potential models, not just those prebuilt into the potfit code. Second, we incorporated the geodesic Levenberg–Marquardt (LM) minimization algorithm into potfit as a new local minimization algorithm. The extended potfit was tested by generating a training set using the KIM environment-dependent interatomic potential (EDIP) model for silicon and using potfit to recover the potential parameters from different initial guesses. The results show that EDIP is a ‘sloppy model’ in the sense that its predictions are insensitive to some of its parameters, which makes fitting more difficult. We find that the geodesic LM algorithm is particularly efficient for this case. The extended potfit code is the first step in developing a KIM-based fitting framework for interatomic potentials for bulk and two-dimensional materials. The code is available for download via https://www.potfit.net.
Highlights
An interatomic potential (IP) is a model for approximating the quantum-mechanical interaction of electrons and nuclei in a material through a parameterized functional form that depends only on the positions of the nuclei
Having established in the previous section that a local minimization is sufficient for environment-dependent interatomic potential (EDIP), we explore the efficiency of Powell’s method, the geodesic LM algorithm added to potfit, and the standard LM algorithm described in [58]
The developer of an IP must select a functional form with adjustable parameters and a suitably weighted training set of first principles and experimental reference data
Summary
An interatomic potential (IP) is a model for approximating the quantum-mechanical interaction of electrons and nuclei in a material through a parameterized functional form that depends only on the positions of the nuclei. As the complexity of IPs increases (both in terms of the functional forms and the number of parameters) it can be difficult to obtain a sufficient number of material properties for the training set This is true for multispecies systems like intermetallic alloys. The issue of insufficient training data is resolved since as many configurations as needed can be generated This makes it possible to increase the number of parameters and in the original Ercolessi–Adams potential for aluminum [7] the functional forms were taken to be cubic splines with the spline knots serving as parameters. We extend the potfit program to support the KIM API making it possible to fit IPs with arbitrary functional forms that are portable to a large number of KIM-compliant simulation codes.
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