Preparing potentials in ASA

To start a calculation you need a starting potential. The GEOMETRYv2/prog directory contains the source code needed for this. This program also calculates the shape functions needed for the FP. It is possible to either start from scratch or from an existing potential. The program calculates the nearest neighbors for each atom, makes a Voronoi construction (possible weights) and then constructs a Voronoi cell for each atom. The ASA sphere will have the same volume as the voronoi cell. Eventually shape functions are constructed which are needed only in FP. The shape functions are set to the given mt-radius and potentials potentials in the obtained radial mesh.

The voronoi.exe needs as input only the inputcard file which contains all the details of the calculation. The program adjusts to ASA or FP, according to the inputcard and geometrical details like the lattice parameters and the position of the atoms and the chemical species of the atoms from the input are also used. If we want to construct the potential from scratch then we leave the potential file name empty in the inputcard (file number I13). In this case the program reads from the directory /ElementDatabase and uses these starting potentials to produce the file name output.pot which contains the starting potential.

In case we have already a potential and we want to use it to start a different calculation then

i) Make with the old potential one iteration using the SKKR using option GENPOT. Produce fort.3 file. This file contains the potential in a generalized form and can be use as input to the voronoi program.

ii) in the new input card we choose as potential file name fort.3. The program reads it and either it just interpolates it in case we want to use an ASA potential for another ASA calculation with a different ASA radius or different lattice constant or produces a potential that can be used for a FP calculation. This last aspect is very useful when we have a difficult system. Do first an ASA calculation and then use the converged ASA potential to start a FP calculation.

In the case of complicated geometries all the atoms do not have the same environment. In this case the 'voronoi' calculates the TB-clusters and in the output file we obtain the number of different clusters and assigns indices to each one. These indices are the values of the CLS parameter that should be now set by the back in the inputcard file, this is not updated automatically. In simple cases like fcc, bcc, sc, all atoms have the same environment so only one TB-cluster is needed. We note here that to understand the structure of the TB-medium we consider a lattice where the same repulsive potential is sitting on each cite independent of the kind of atom the occupies that cite.