ONETEP

ONETEP [1], the order-N electronic total energy package is a numerical implementation of Density Functional Theory. Unlike usual implementations of DFT, the computational resources required for the calculation of the energy of a particular atomic system scales linearly with the number of electrons, which makes it exceptionally efficient in investigations of large systems. However, in our work we exploited another feature of ONETEP, namely, that it uses local basis functions. 

In ONETEP, Wannier functions are constrained in a localisation sphere centred on atoms, i.e. = 0 outside the localisation sphere, providing an atomic basis set. The radius of the localisation sphere is set by considering the electronic structure of the system or it can be increased until convergence of the physical properties is achieved. The nonorthogonal Wannier functions are optimised during the electronic structure calculation, hence they represent the best possible atomic basis functions of a particular system. In our studies of the atomic properties, we used these Wannier functions as the atomic basis set for calculating atomic properties with our definition for these properties given in Eq. 6.8. 

As a test system, we used clusters of 29-71 silicon atoms. The configurations were generated by molecular dynamics simulation at 3,000 K, where the forces were obtained from the StiUinger—Weber potential [4]. We performed the electronic structure calculations of the different clusters using ONETEP, and we also used ONETEP to determine the atomic energies, as described in Sect. 6.1.2. A typical cluster is shown in Fig. 6.1. 

ONETEP Linear-Scaling Density-Functional Theory with Local Orbitals and Plane Waves. 

Skylaris, C.-K., Haynes, P. D., Mostofi, A. A., Payne, M. C. (2005). Introducing ONETEP Linear-scaling density functional simulations on parallel computers. Journal of Chemical Physics, 122, 084119. 

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