On the ab initio calculation of vibrational formation entropy of point defect: the case of the silicon vacancy
1 Institut Photovoltaïque d’Ile-de-France (IF), 8, rue de la Renaissance, 92160 Antony, France
2 Institute for Research and Development of Photovoltaic Energy (IRDEP), UMR 7174 CNRS/EDF R&D/Chimie ParisTech-PSL, 6 quai Watier, 78401 Chatou, France
3 EDF R&D, Departement EFESE, 6 Quai Watier, 78401 Chatou, France
Received: 4 November 2016
Accepted: 13 June 2017
Published online: 1 August 2017
Formation entropy of point defects is one of the last crucial elements required to fully describe the temperature dependence of point defect formation. However, while many attempts have been made to compute them for very complicated systems, very few works have been carried out such as to assess the different effects of finite size effects and precision on such quantity. Large discrepancies can be found in the literature for a system as primitive as the silicon vacancy. In this work, we have proposed a systematic study of formation entropy for silicon vacancy in its 3 stable charge states: neutral, +2 and –2 for supercells with size not below 432 atoms. Rationalization of the formation entropy is presented, highlighting importance of finite size error and the difficulty to compute such quantities due to high numerical requirement. It is proposed that the direct calculation of formation entropy of VSi using first principles methods will be plagued by very high computational workload (or large numerical errors) and finite size dependent results.
© P. Seeberger and J. Vidal, published by EDP Sciences, 2017
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