Electronic structure of materials under pressure

Abstract

Parameter-free calculations based on the density-functional theory are used to examine high-pressure phases of solids. For the elemental semiconductors, as represented by Si, the high-pressure phases are examined in some detail, and particular attention is paid to the Si(VI)orthorhombic (Cmca) structure which was resolved only very recently. For III-V semiconductors the optimization of the structural parameters of the Cmcm and Imm2 phases is described. The structural energy differences are in several cases very small, and in some cases too small to allow a safe structure prediction on the basis of the calculations. In that context we also discuss ways to go beyond the local density approximation (LDA). We show that the predicted high-pressure phases may be significantly affected by inclusion of (generalized) gradient corrections (GGA). Elemental Zn (hcp) is further taken as an example where we find that the simple LDA leads to poor results for the equilibrium volume and axial ratio (c/a). Introducing corrections, for example by GGA, it is, however, possible to achieve an accuracy that allows a study of the structural changes of Zn (and Cd) under pressure and analysis of these changes in terms of electronic topological transitions.

Structural and electronic properties of Mg, Zn, and Cd from Hartree-Fock and density functional calculations including hybrid functionals

“…12 However, these results are heavily dependent on the choice of the computational parameters. [23][24][25][26][27][28][29][30][31][32][33] Novikov et al 23 have noticed that the equilibrium volume is underestimated by Ϸ10% when applying the local density approximation ͑LDA͒. They proposed several enhancements of the LDA, self-interaction correction, downshift of d-states, to improve the results.…”

Ab initiocorrelation calculations for the ground-state properties of group-12 metals Zn and Cd

“…[1][2][3][4][5][6][7][8][9][10][11] However, all of these calculations are performed within the framework of density functional theory ͑DFT͒ treating the electronic correlations implicitly with various functionals. A recent publication 12 proved that none of the functionals including the recent hybrid functionals give entirely satisfactory results, although certain functionals reproduce a few properties.…”

Calculations of quasi‐particle spectra of semiconductors under pressure

“…The local density approximation (LDA) 1 to the density‐functional theory 2 has been extremely successful in connection with prediction of ground state properties of a large number of materials, structural, magnetic, vibrational properties including pressure effects (structural transformations 3, 4 and superconductivity, Refs. 5, 6 and references therein).…”

“…A well‐known problem is the so‐called “LDA gap error” in band structures of semiconductors, where the LDA underestimates the band gap by 50–100%. Another problem, which in fact also affects ground‐state properties, and which is related to underestimation of correlation, is the rather poor description of more localized semi‐core states, like the 3d states in Zn 3, 4 and Zn compounds. Errors in the spectral position of such states affect the modeling of photoemission spectra and the states at the top of the valence band via hybridization, i.e., they also contribute to the “LDA gap error.” LDA + U methods 7–9 are some ways to correct for this, and here copper aluminate, CuAlO 2 , is chosen as an example where this problem is particularly pronounced.…”