Heats of formation of GeH 4 , GeF 4 and Ge(CH 3 ) 4 Hideya Koizumi * , Juan Z. Da ´valos 1 , Tomas Baer Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-3290, United States Received 9 August 2005; accepted 2 November 2005 Available online 28 November 2005 Abstract The heats of formation of GeH 4 , GeF 4 , and Ge(CH 3 ) 4 are computed at CCSD(T) level of theory at the complete basis set limit. Rel- ativistic effects, core valence correlation, spin orbit effect, and zero point energy are explicitly calculated in this study. Relativistic recov- eries for these molecules are investigated with different size of correlation space. An unusually large relativistic effect is observed in GeF 4 . Our best calculated geometries for GeH 4 and GeF 4 are in excellent agreement with the high precision experiments. Anharmonic correc- tion to the zero point energy is significant for Ge(CH 3 ) 4 . Our best calculated values for the 298 K heats of formation of GeH 4 , GeF 4 , and Ge(CH 3 ) 4 are 82, 1194, and 123 kJ/mol, respectively. Ó 2005 Elsevier B.V. All rights reserved. Keywords: Ab initio methods; Relativistic effect; Heat of formation; GeH 4 ; GeF 4 and Ge(CH 3 ) 4 1. Introduction Germanium thin films, isovalent with carbon and sili- con, have been used in the semiconductor industry for a number of years. Germanium is used primarily for spe- cialty applications such as in transistor elements. The Ge layers are generally deposited by chemical vapor deposition (CVD) using mostly Germane (GeH 4 ). However, other Ge containing molecules could also be employed. Low-temper- ature thermal chemical vapor deposition reported by Zhang et al. [1] uses a gas-phase mixture of Si 2 H 6 and GeF 4 . Fajgar et al. [2] investigated CO 2 laser SF 6 -photo- sensitized decomposition of tetramethyl germanium for potential use in Ge CVD film precursors. These CVD pro- cess have been studied fairly extensively for last decade for use in semiconductor applications. Although the bond energies of the reagent molecules are clearly important in the CVD process, relatively little is known about the thermochemistry of Ge containing molecules. Even the heat of formation of germane (GeH 4 ), the simplest tetravalent Ge molecule is not well established. The only experimental heat of formation of GeH 4 (90.3 ± 2 kJ/mol at 298 K) was determined by bomb calorimetry more than 40 years ago [3]. On the other hand, several GeH 4 theoretical investigations have been reported, among them a Gaussian n theory study, a popular method known to give very accurate results for molecules consisting of first and second row atoms. Modified G1 results of Binning and Curtiss [4], G2 results of Mayer et al. [5], G3 results of Curtiss [6], and G3/DFT results of Wang and Zhang [7] have also been reported. Ramakrishna and Duke [8] used complete basis set meth- ods (CBS-X) to obtain the total atomization energy of GeH 4 . Their atomization energies for several CBS deriva- tives gave values of 19–40 kJ/mol larger than the experi- ment values. Recently, Yockel et al. [9] studied germane using coupled cluster theory as well as density functional theory in the complete basis set limit as part of a system- atic comparison of performance between ab initio and density functional theory. In their second bench mark paper [10], they explicitly consider the relativistic effect which is known to be important for molecules containing third row atoms. Ricca and Bauschlicher [11] studied 0301-0104/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.chemphys.2005.11.002 * Corresponding author. E-mail address: koizumi@email.unc.edu (H. Koizumi). 1 Instituto de Quimica-Fisica ‘‘Rocasolano’’, CSIC, Serrano 119, 28006, Madrid, Spain. www.elsevier.com/locate/chemphys Chemical Physics 324 (2006) 385–392