Eur. Phys. J. D (2012) 66: 105
https://doi.org/10.1140/epjd/e2012-20737-9

Regular Article

Density functional study of low-lying isomers of SiO₄, GeO₄ and CO₄, and their relation to tetrahedral solid phases

¹ Departamento de Física Teórica, Atómica y Óptica, Universidad de Valladolid, 47005 Valladolid, Spain
² Department of Physics, University of Antwerp, Antwerp, Belgium
³ Oxford University, Oxford, England

^a e-mail: cabria@fta.uva.es

Received: 16 December 2011
Published online: 30 April 2012

Abstract

In silica (SiO₂) and in most silicates, atomic associations exist with composition SiO₄ and a structure with four O atoms in tetrahedral coordination around the Si atom. A similar feature is observed in germania (GeO₂) and some solids containing Ge instead of Si, although the number of phases containing GeO₄ tetrahedra is smaller. In contrast, and in spite of the fact that C is in the same column of the periodic table as Si and Ge, CO₂ is a molecular solid, and crystalline and amorphous phases of CO₂ showing CO₄ tetrahedra are only obtained under extremely high pressures. We have investigated the relation between free SiO₄, GeO₄ and CO₄ clusters and the tetrahedral associations found in the solids mentioned above. The lowest energy structure of those three free clusters is planar, but they have near-tetrahedral and distorted-tetrahedral isomers. The promotion energy from the planar structure to the distorted tetrahedral is low in SiO₄, large in CO₄, and intermediate in GeO₄. This correlates with the facility to form tetrahedral associations in the solids.