Ab initio total-energy pseudopotential calculations for polymorphic B2O3 crystals.

8 0 is an interesting material, showing two po2 3 lymorphs in which the boron atoms have different coordination numbers (see Figs. 1 and 2). Neither form of crystalline trioxide occurs naturally. Furthermore, it is not easy even under special conditions to prepare crystals and asure their properties. In such cases computer simulations can play an important role in determining t e structural and physical properties. Advances in the techniques of electronic-structure calculations make it possible to calculate total energies with high accuracy. These computer simulation techniques are currently used to study not only static but also dynamical structures in both the crystalline and amorphous states, although there are still considerable limitations on the size of a system that can be studied (in particular, the number of independent atoms in the unit cell) because of the constraints imposed by computer resources. In a companion study' of 8203 and borates using periodic ab initio Hartree-Fock techniques, we provide a consistent interpretation of the structure and bonding o borates which accords well with empirical concepts regarding the structure and bonding in these crystals. However, these methods were unable to study fully relaxed structures in detail, as automatic relaxation o ce11 dimensions or internal coordinates is not available in the present version of the periodic ab initio Hartree-Fock program (CRYSTAL92). In this paper we discuss how the structures and bulk