To save the shell positions, one must choose a file format that supports shell model, like the GULP input file or the DL_POLY formats:Ītomsk NaCl.xsf -add-shells all NaCl_shells.gin It is important to bear that in mind when dealing with core-shell model: beware that if you output your system to a file format that does not support shell model, then the shells are simply lost. The reason is simple: the XSF file format does not support shells, so it is impossible to write shell positions in such a file. Now if you open the final file ('NaCl_shells.xsf') in a text editor, you will notice that it does not contain any shell. Shells can be added to all ions in an existing system, thanks to the option '-add-shells':Ītomsk NaCl.xsf -add-shells all NaCl_shells.xsf Shells are stored in a separate array, and always have the same index as their associated core.įor the following, let us create a unit cell of an ionic material like sodium chloride, NaCl:Ītomsk -create rocksalt 5.64 Na Cl xsf 1. If the core and shell are at the same position then the ion is not polarized if they are at different positions, then the ion is polarized (because the centers of positive and negative charges do not coincide).Īlthough Atomsk is not aware of the shell-model potential itself, it is capable of dealing with the position and electric charge of shells.

In such a model, each ion is composed of two particles: its core that is massive and has a charge Q, and a shell that mimics the electronic cloud, that is massless (or has a small mass, depending on the type of shell model) and has a charge q. Ionic core-shell models are a type of classical empirical potential, often used to describe polarizable ionic materials. This tutorial explains how to create and manipulate systems that contain shells, for the purpose of atomistic simulations with an ionic core-shell model.

Mimics tutorial