Ab initiomodeling of surface structure forSrTiO3perovskite crystals

Abstract

We present and discuss the results of calculations of SrTiO 3 ͑100͒ surface relaxation and rumpling with two different terminations ͑SrO and TiO 2 ͒. These are based on ab initio Hartree-Fock method with electron correlation corrections and density functional theory calculations with different exchange-correlation functionals, including hybrid exchange techniques. Both approaches use the localized Gaussian-type basis set. All methods agree well on surface energies and on atomic displacements, as well as on considerable increase of covalency effects nearby the surface. More detailed experiments on surface rumpling and relaxation are necessary for further testing theoretical predictions.

Ab initiocalculations of the atomic and electronic structure ofCaTiO3(001) and (011) surfaces

“…24 The amplitude of the surface rumpling on the CaO-terminated surface is predicted to be almost five times larger than that for the TiO 2 -terminated (001) one. From Table III, one can see that both CaTiO 3 (001) surfaces show a reduction of interlayer distance ∆d 12 and an expansion of ∆d 23 . The reduction of interlayer distance ∆d 12 is twice as large for the CaO-terminated surface than it is for the TiO 2 -terminated surface.…”

“…32 where the second-layer anion (Pb or Ba) relaxations were larger than the upper-layer (Ti or Zr) ones. In order to compare the calculated surface structures with experimental results, the surface rumpling s (the relative oxygen displacement relative to the metal atom in the surface layer) and the changes in interlayer distances ∆d 12 and ∆d 23 (where 1, 2 and 3 label the nearsurface layers) are presented in Table III. Our calculations of the interlayer distances are based on the positions of the relaxed metal ions (Fig.…”

“…Here we employ this BS, which differs from that used in Refs. [12,13] by inclusion of polarizable d-orbitals on O ions. It was shown 44 that this leads to better agreement of the calculated lattice constant and bulk modulus with experimental data.…”

“…With the sole exception of the calculation on CaTiO 3 by Zhang et al, 6 all of the first-principles and shell-model studies of ABO 3 perovskite surface energies 7,12,16,23,30,32,42 have found that the lowestenergy (001) surface is lower in energy than any of the (011) terminations. Zhang et al, 6 on the contrary, reported a surface energy of 0.837 eV for their "A-type" O-terminated (011) surface of CaTiO 3 , to be compared with 1.021 eV for the TiO 2 -terminated (001) surface.…”

“…For the CaTiO 3 (001) surface we are only aware of the work of Wang et al 5 and Zhang et al 6 In contrast, several other ABO 3 perovskite (001) surfaces have been widely studied. For example, ab initio 7,8,9,10,11,12,13,14,15,16,17,18,19,20,21 and classical shell-model 22,23 studies were published for the (001) surfaces of SrTiO 3 . The (001) surfaces of cubic perovskites have also been extensively investigated experimentally.…”