抄録
The internal energy of As is investigated as a function of the volume and structure parameters by using the pseudopotential expansion method. In the calculation Topp-Hopfield’s potential fitted to atomic energy levels in As4+ is used. The second order approximation describing metallic part of the bonding does not give a stable A7 structure and, in order to get a stable A7 structure, it is indispensable to take account of the third order contribution including covalent part. The crystal energy and atomic volume of the A7 structure in equilibrium at zero pressure are calculated to be −12.559 ryd/atom and 2.26×10−23 cm3, which are compared with experimental values −12.675 ryd/atom and 2.13×10−23 cm3. The dependence of the internal strain from simple rhombohedral to A7 on the separation of atomic s and p terms is discussed in relation to the chemical valency.
