A method for accurate and efficient local density functional calculations (LDF) on molecules is described and presented with results. The method, Dmol for short, uses fast convergent three-dimensional numerical integrations to calculate the matrix elements occurring in the Ritz variation method. The flexibility of the integration technique opens the way to use the most efficient variational basis sets. A practical choice of numerical basis sets is shown with a built-in capability to reach the LDF dissociation limit exactly. Dmol includes also an efficient, exact approach for calculating the electrostatic potential. Results on small molecules illustrate present accuracy and error properties of the method. Computational effort for this method grows to leading order with the cube of the molecule size. Except for the solution of an algebraic eigenvalue problem the method can be refined to quadratic growth for large molecules.

Recent extensions of the DMol3 local orbital density functional method for band structure calculations of insulating and metallic solids are described. Furthermore the method for calculating semilocal pseudopotential matrix elements and basis functions are detailed together with other unpublished parts of the methodology pertaining to gradient functionals and local orbital basis sets. The method is applied to calculations of the enthalpy of formation of a set of molecules and solids. We find that the present numerical localized basis sets yield improved results as compared to previous results for the same functionals. Enthalpies for the formation of H, N, O, F, Cl, and C, Si, S atoms from the thermodynamic reference states are calculated at the same level of theory. It is found that the performance in predicting molecular enthalpies of formation is markedly improved for the Perdew–Burke–Ernzerhof [Phys. Rev. Lett. 77, 3865 (1996)] functional.

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The complete atomic structure of a five-monolayer film of LaAlO3 on SrTiO3 has been determined for the first time by surface x-ray diffraction in conjunction with the coherent Bragg rod analysis phase-retrieval method and further structural refinement. Cationic mixing at the interface results in dilatory distortions and the formation of metallic La(1-x)SrxTiO3. By invoking electrostatic potential minimization, the ratio of Ti{4+}/Ti{3+} across the interface was determined, from which the lattice dilation could be quantitatively explained using ionic radii considerations. The correctness of this model is supported by density functional theory calculations. Thus, the formation of a quasi-two-dimensional electron gas in this system is explained, based on structural considerations.

A method is presented for efficient calculation of the electrostatic potential due to the nuclei and the continuous electronic charge distribution in a crystal or a large molecule. Accuracy is under the control of a single tolerance parameter. The computational cost for the calculation of the static potential on the entire grid and for static energy evaluation scales asymptotically as O(N) with a favorable prefactor.

* These authors contributed equally to this work.The future prosperity of information technology strongly depends on creating new device concepts with improved functionality and on successfully scaling of their characteristic lengths.[1] The spectrum of attractive novel non-volatile memory technologies currently being explored to sustain the increase of functionality in semiconductor devices ranges from magnetic random-access-memory [2,3] and chalcogenide phase-change memory [4,5] to resistance-change memory based on transition-metal-oxides. [6][7][8] The latter compounds can be conditioned such that they exhibit a bistable resistance state. The microscopic origin of the resistance-change memory in these transition-metal oxides is not understood. Here we investigate the relevance of oxygen vacancies for the resistance-change memory using the transitionmetal oxide chromium-doped strontium titanate (Cr-doped SrTiO 3 ) as example.Laterally resolved micro-x-ray absorption spectroscopy and infrared thermal microscopy demonstrate that the conditioning process creates an electrically conducting path with a high density of oxygen vacancies which are localized at a Cr ion. Both

Following on from the earlier work of Pulay and Fogarasi [J. Chem. Phys. 96, 2856 (1992)] we present an alternative definition of natural internal coordinates. This set of delocalized internal coordinates can be generated for any molecular topology, no matter how complicated, and is fully nonredundant. Using an appropriate Schmidt-orthogonalization procedure, all standard bond length, bond angle, and dihedral angle constraints can be imposed within our internal coordinate scheme. Combinatorial constraints (in which sums or differences of stretches, bends, and torsions remain constant) can also be imposed. Optimizations on some fairly large systems (50–100 atoms) show that delocalized internal coordinates are far superior to Cartesians even with reliable Hessian information available at the starting geometry.