Graduate Module - First Principles Materials Modelling

Assessment

There will be one formative mini-assignment, set at the end of the introductory material, based upon work done in the practical classes). This will be worth 20% of the module mark.

There will be one major summative assignment, set at the end of the advanced material, which will take an additional 6 weeks, based upon using CASTEP to solve a research-level challenge, with appropriate write- up in the form of a short paper. This will be worth 80% of the module mark.

You should submit all your work using the VLE.

Mini Assignment 1

Here are three different cell files for silicon:

These contain ONLY an initial guess at the lattice parameters and atomic coordinates for the primitive cell of 3 different crystal structures.

Your task is to compute the variation in stability with pressure (NOT temperature - keep T=0 and do not include phonons or dynamical information) of these three different silicon structures, and produce a prediction of which phase is most stable under which pressure from 0 - 100 GPa. Hence your conclusion might be `A is most stable at P=0; there is a pressure-driven phase transition to B at P=30 GPa. C is never more stable than A or B up to P=100 GPa.' Or something quite different!

To do this, you will need to create appropriate param files, add extra bits to the cell files, and run a series of calculations. You should make use of the lecture material covered in week 1 only - there is no need for anything from week 2.

You should submit a brief report (in PDF format) of what you have done and your conclusions (min 2 sides A4, max 5 sides A4, including figures). Make sure you include enough information that the reader will be convinced of the quality of your calculations, and be able to reproduce the final conclusion.

Hand in 16:00 Friday 7 October using VLE.

Mini Assignment 2

Consider the 64-atom cell file for a particular high-pressure silicon phase give below. This contains ONLY an initial guess at the lattice parameters and atomic coordinates of the system and has NOT been relaxed. A second file contains the same structure but with one atom missing, ie a point defect vacancy. This too has NOT been relaxed:

Your tasks are:

Compute the formation energy for the uncharged vacancy point defect.
Compute a 'fingerprint' of the defect, using ONE of NMR, EELS or IR spectrum, comparing the defect (63-atom) vs perfect (64-atom) structure.

You do NOT need to consider finite size effects, hence you should not consider supercells of the structure given. You should only use a GGA functional.

Hand in 17:00 Friday 21 October using VLE.