Posted by Coen de Graaf on November 10, 2005 at 10:17:59:
In Reply to: Embedded cluster question posted by Serhii Galunic on November 09, 2005 at 18:45:33:
You only need to specify the symmetry unique point charges. Seward will generate all the other charges.
There are several possibilities to generate arrays of point charges to incorporate the Madelung field in your cluster calculation. The simplest one is the Evjen method (formal ionic charges at the lattice positions within a large box around the cluster and fractional charges at the faces, edges and corners). However, this methd has the inconvenience that it only works well for simple cubic lattices, see for example: C. Sousa et al., Journal of Computational Chemistry 14, 680 (1993) and Derenzo et al, J. Chem. Phys. 112, 2074 (2000). The second method is the optimization of a small number of point charges so that they accurately reproduce the Madelung potential in the cluster region. There are several codes around to do this. The one I use works rather well, but is not very user-friendly (it is quite an old code). The one of Derenzo et al (Computer Physics Communications 131, 120 (2000) is much easier to use, but does not maintain the symmetry of the cluster in the point charge array.
All the best,
Coen