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In the series of 3d1 t2g perovskites, SrVO3--CaVO3--LaTiO3--YTiO3 thetransition-metal d electron becomes increasingly localized and undergoes a Motttransition between CaVO3 and LaTiO3. By defining a low-energy HubbardHamiltonian in the basis of Wannier functions for the t2g LDA band and solvingit in the single-site DMFT approximation, it was recently shown[1] thatsimultaneously with the Mott transition there occurs a strong suppression oforbital fluctuations due to splitting of the t2g levels. The present paperreviews and expands this work, in particular in the direction of exposing theunderlying chemical mechanisms by means of ab initio LDA Wannier functionsgenerated with the NMTO method. The Wannier functions for the t2g band exhibitcovalency between the transition-metal t2g, the large cation-d, and theoxygen-p states; this covalency, which increases along the series, turns out tobe responsible not only for the splittings of the t2g levels, but also fornon-cubic perturbations of the hopping integrals, both of which are decisivefor the Mott transition. We find good agreement with the optical andphotoemission spectra, with the crystal-field splittings and orbitalpolarizations recently measured for the titanates, and with the metallizationvolume for LaTiO3. The metallization volume for YTiO3 is predicted. Usingsuper-exchange theory, we reproduce the observed magnetic orders in LaTiO3 andYTiO3, but the results are sensitive to detail, in particular for YTiO3 which,without the Jahn-Teller distortion, would be AFM C- or A-type, rather than FM.Finally, we show that it possible to unfold the orthorhombic t2g LDAbandstructure to a pseudocubic zone. In this zone, the lowest band is separatedfrom the two others by a direct gap and has a width, W_I, which issignificantly smaller than that, W, of the entire t2g band. The progressiveGdFeO3-type distortion favours electron localization by decreasing W, byincreasing the splitting of the t2g levels and by decreasing W_I. Ourconclusions concerning the roles of GdFeO3-type and JT distortions agree withthose of Mochizuki and Imada [2].

How chemistry controls electron localization in 3d1perovskites: a Wannier-function study

How chemistry controls electron localization in 3d¹perovskites: a Wannier-function study