Recent developments in and around the SIESTA method of first-principles simulation of condensed matter are described and reviewed, with emphasis on (i) the applicability of the method for large and varied systems, (ii) efficient basis sets for the standards of accuracy of density-functional methods, (iii) new implementations, and (iv) extensions beyond ground-state calculations.

We used first-principles methods to perform a systematic search for potentially-stable phases of multiferroic BiFeO3. We considered a simulation cell compatible with the atomic distortions that are most common among perovskite oxides, and found a large number of local minima of the energy within 100 meV/f.u. of the ferroelectric ground state. We discuss the variety of low-symmetry structures discovered, as well as the implications of these findings as regards current experimental (e.g., on thin films displaying {\em super-tetragonal} phases) and theoretical (on models for BiFeO3's structural phase transitions) work on this compound.Comment: 14 pages, 9 figures, accepted in PRB (contains small changes in the text with respect to the first version

Using an extension of a first-principles method developed by King-Smith and Vanderbilt [Phys. Rev. B 49, 5828 (1994)], we investigate the effects of in-plane epitaxial strain on the groundstate structure and polarization of eight perovskite oxides: BaTiO3, SrTiO3, CaTiO3, KNbO3, NaNbO3, PbTiO3, PbZrO3, and BaZrO3. In addition, we investigate the effects of a nonzero normal stress. The results are shown to be useful in predicting the structure and polarization of perovskite oxide thin films and superlattices.

We present a reformulation of the plane-wave pseudopotential method for insulators. This new approach allows us to perform density-functional calculations by solving directly for ''nonorthogonal generalized Wannier functions'' rather than extended Bloch states. We outline the theory on which our method is based and present test calculations on a variety of systems. Comparison of our results with a standard plane-wave code shows that they are equivalent. Apart from the usual advantages of the plane-wave approach such as the applicability to any lattice symmetry and the high accuracy, our method also benefits from the localization properties of our functions in real space. The localization of all our functions greatly facilitates the future extension of our method to linear-scaling schemes or calculations of the electric polarization of crystalline insulators.

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