Choosing models for solids

The atomistic simulation of properties and phenomena in solid materials req uires a suitable model of the real system with a number of atoms which is s till manageable at the chosen level of approximation. Since typical solids consist of atoms in the order of 10(23), only a very small fraction of them can be treated explicitly. The effect of the rest on the explicitly treate d part has to be taken into account somehow. This paper attempts to categor ize and explain the various tricks applied in modeling solids, showing thei r strength and weakness.