Direct wide band gap material: a Hartree±Fock study of a-Be 3 N 2 Ma. Guadalupe Moreno Armanta a,b, * , Armando Reyes-Serrato c a Centro de Ciencias de la Materia, Condensada, UNAM, P.O. Box 439036, San Ysidro, CA 92143, USA b Programa de Posgrado en F  õsica de Materiales del Centro, de Investigaci on Cient  i®ca y de Educaci on Superior de Ensenada, Km. 107 Carretera Tijuana-Ensenada, Mexico c Centro de Ciencias de la Materia Condensada de la UNAM, Apartado Postal 2681, Ensenada B.C., 22800, Mexico Received 18 May 2000; received in revised form 10 October 2000; accepted 13 November 2000 Abstract The ground state electronic structure of the beryllium nitride alpha phase has been investigated using the all-electron ab initio periodic Hartree±Fock HF) approach, with a posteriori density-functional DFT) correlation corrections. The computed HF lattice constant 8.144  A) agrees with experiment 8.145  A) and the calculations predict a bulk modulus of 2.52 Mbar and cohesive energy of 1.24 a.u./formula unit. The band gap is found to be direct of 4.43 eV at the C point, including corrections with DFT. This material might have application in the area of optoelectronics. Ó 2001 Elsevier Science B.V. All rights reserved. PACS: 71.15.Fv; 71.15.Nc; 71.20.)b Keywords: Ab initio; Hartree±Fock theory; Electronic structure; Wide band gap; Beryllium nitride; Direct band gap; Nitride; LCAO 1. Introduction The development of wide band gap materials has been stimulated by the demand for optical devices, such as light-emitting diodes and laser diodes operating in the green±blue near UV re- gion. For these materials, the main activities have been in II±VI compounds for several years. Ad- ditionally, III±V nitride semiconductors such as GaN have been investigated intensively for a long time [1,2]. Great interest in wide band gap nitrides is due to possible applications in blue/UV light emitting diodes and lasers and in high temperature elec- tronics [3,4]. The development in the search for materials has been focused mainly in the investigation of the electrical properties of large number of binary compounds with their crystal structure similar to either one of the cubic mineral sphalerite or to hexagonal wurtzite. These compounds belong to one of the three types, III±V, II±VI, or I±VII. The average number of valence electrons per atom, in compounds of these types is equal to four, the same as in the group IV elements; each atom in the www.elsevier.com/locate/commatsci Computational Materials Science 21 2001) 95±100 * Corresponding author. Tel.: +1-52-617-44602; fax: +1-52- 617-44603. E-mail addresses: moreno@ccmc.unam.mx M. Guadalupe Moreno Armanta), armando@ccmc.unam.mx A. Reyes- Serrato). 0927-0256/01/$ - see front matter Ó 2001 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 7 - 0 2 5 6  0 0 ) 0 0 2 2 0 - 2