Calculation of thermal properties of diamond from simulated phonon spectra Irina Rosenblum a,b , Joan Adler a, * , Simon Brandon b a Department of Physics, Technion-IIT, 32000 Haifa, Israel b Department of Chemical Engineering, Technion-IIT, 32000 Haifa, Israel Received 14 January 1998; accepted 26 March 1998 Abstract A method for the calculation of thermal properties of dielectric materials, based on determination of the mode density of states directly from phonon spectra (PS), and allowing the systematic study of the eect of dierent pa- rameters on thermal properties, is proposed. The initial phonon spectra are obtained using the molecular dynamics (MD) simulation technique. This method is applied to diamond modeled with the Brenner potential and is illustrated by the analysis of the eect of low frequency modes, sample size, temperature and the type of incorporated defects, on diamond heat capacity and thermal conductivity; the revealed tendencies agree with experiment. Values obtained from the PS method are compared to those directly measured by MD, and the advantages of the former method of calcu- lation are discussed. Ó 1998 Elsevier Science B.V. All rights reserved. PACS: 63.20.-e; 63.20.Mt; 66.70.+f; 65.40.+g; 02.70.Ns Keywords: Diamond; Molecular dynamics; Phonon spectra; Calculation of thermal properties; Defects 1. Introduction Carbon, both pure and in compounds involving other elements, is a fascinating material. Its capa- bility to exist in diamond and graphite forms, as well as to produce intermediate amorphous phases and to generate chemical compositions with hy- drogen, allows the creation of an almost unlimited variety of structures with a wide range of physical properties that are useful for many dierent tech- nological applications. Experimental analysis of carbon is limited in its ability to provide detailed understanding of atomic level processes. This has created a need for theoretical structure simulations of carbon. These have been intensely pursued in the past two decades; a recent review of computer simulations of carbon-based materials can be found in [1]. Within the carbon-based materials diamond stands out owing to its exceptionally strong bonds which give unique chemical and physical proper- ties. One property of particular importance is its high thermal conductivity at room temperature, which results from the stiness of the diamond- bond and from this material's high Debye tem- perature [2]. However, this high thermal conductivity is known to be considerably reduced by the various defects, isotopes and inclusions that are present in both natural and synthetic diamond [3]. In experiments it is dicult to achieve a Computational Materials Science 12 (1998) 9±25 * Corresponding author. Tel.: +972-4-8293937; fax: +972-4- 8221514; e-mail: phr76ja@phjoan.technion.ac.il. 0927-0256/98/$ ± see front matter Ó 1998 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 7 - 0 2 5 6 ( 9 8 ) 0 0 0 1 5 - 9