**Chris Eames**

This document is a basic introduction to the methodology of performing geometry optimisation calculations with the
CASTEP program. It is not intended as a review of the ideas behind that methodology. Before approaching this guide the
reader is strongly recommended to read a relevent review article (such as [1] or [2]) if they do not have the
background knowledge.

The aim of this guide is to answer three questions;

- What structures can be geometry optimised and what types of geometry optimisation are there?
- What are the basic inputs to a calculation and how are they set up?
- What are the possible outputs of a calculation and how should they be interpreted?

- Recipe
- Inputs
- The .cell file and Pseudopotential libraries
- The Size and Shape of the Supercell
- The Initial Configuration of the Atoms Within the Supercell
- The k-point sampling grid
- Cell symmetry
- Constraints on the cell size/shape
- Constraints on the movement of ions
- Atomic masses
- The location of the pseudopotential libraries
- External pressure that is to be applied to the supercell

- The .param file

- The .cell file and Pseudopotential libraries
- Example - Bulk Silicon
- Outputs

- Checking the absolute convergence of our Bulk Silicon Calculation
- A Variable Cell calculation for Bulk Silicon.
- Example - A Bulk Terminated Silicon Surface
- References
- About this document ...

2005-04-04