Dresden 2011 – scientific programme

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O: Fachverband Oberflächenphysik

O 74: Focussed session: Theory and computation of electronic structure: new frontiers VI (jointly with HL, DS)

O 74.5: Talk

Thursday, March 17, 2011, 16:00–16:15, TRE Phy

First-principle approach to the temperature dependence of electronic energies. — Paul Boulanger^{1, 2}, Michel Cote², and •Xavier Gonze¹ — ¹ETSF / IMCN, Université Catholique de Louvain, 1 Place Croix du Sud, B-1348 Louvain-la-Neuve, Belgium — ²Département de physique, Université de Montréal, C.P. 6128, succ. Centre-ville, Montréal (Québec) H3C 3J7, Canada

The energy bands of semiconductors exhibit significant shifts with temperature, due to electron-phonon interactions. In search of an efficient first-principle approach to this effect, we have found that formulas derived by Allen, Heine and Cardona in a semi-empirical context cannot be transposed to Density-Functional Theory or to Many-Body Perturbation Theory without critical reexamination. For these theories, the correct formulation includes a extra term, the non-site-diagonal Debye-Waller term, which is dependent on second-order derivatives of the self-consistent electron-lattice potential with respects to atomic displacements. We have studied the importance of this extra term for diatomic molecules and found that it partially cancels the standard Debye-Waller and Fan terms leading a decrease by 52% for H2, 10% for N2 and 37% for LiF. For CO it adds about 15% to the temperature dependence. The lack of this term might explain the discrepancy found between previous theory and experiment for solids. Furthermore, the slow convergence of the sum-over-states approach of Allen-Heine-Cardona approach can be avoided in a new formalism proposed here, based on Density-Functional Perturbation Theory, leading to a dramatic decrease of calculation times.