next up previous contents
Next: Population Analysis Up: The Total Energy Pseudopotential Previous: Charged Molecules



This chapter has described the theoretical framework for the calculations performed in this thesis. Sections gif and gif outlined the conceptual problem and an approach to its solution, namely Density Functional Theory. Sections gif though gif described a series of approximations made so that the calculations may be performed in a reasonable time with good accuracy. These approximations may be summarised as follows:

These approximations differ from those made in non-first principles approaches in that they depend on general physical and chemical principles and not on the specific interactions within the system to be investigated. Section gif described a correction to the conventional pseudopotential approximation that gives greater accuracy when considering spin dependent potentials.

The implementation of this method for finding the ground state energy and charge density was discussed in Sections gif and gif. Once these quantities have been found, the ionic forces may be calculated and used as explained in Section gif. Finally, a post-hoc correction to the results obtained for charged systems was detailed in Section gif.

The methods described in this chapter have been implemented in the CASTEP [5] code for serial and vector computers and the CETEP [42] code on parallel machines. These codes have been used for all of the calculations described in this thesis.

Matthew Segall
Wed Sep 24 12:24:18 BST 1997