F. Vila

Publications (4)0 Total impact

• Source

  Available from: J. J. Rehr

  Article: Theoretical optical and x-ray spectra of liquid and solid H_2O

  J. Vinson, J. Kas, F. Vila, J. J. Rehr, E. L. Shirley
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  ABSTRACT: Theoretical optical and x-ray spectra of model structures of water and ice are calculated using a many-body perturbation theory, Bethe-Salpeter equation (BSE) approach implemented in the valence- and core-excitation codes AI2NBSE and OCEAN. These codes use ab initio density functional theory wave functions from a plane-wave, pseudopotential code, quasi-particle self energy corrections, and a BSE treatment of particle-hole interactions. The approach improves upon independent-particle methods through the inclusion of a complex, energy-dependent self energy and screened particle-hole interactions to account for inelastic losses and excitonic effects. These many-body effects are found to be crucial for quantitative calculations of ice and water spectra.
  10/2011;
• Source

  Available from: Jeffrey P. Gardner

  Article: Scientific Computing in the Cloud

  J. J. Rehr, J. P. Gardner, M. Prange, L. Svec, F. Vila
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  ABSTRACT: We investigate the feasibility of high performance scientific computation using cloud computers as an alternative to traditional computational tools. The availability of these large, virtualized pools of compute resources raises the possibility of a new compute paradigm for scientific research with many advantages. For research groups, cloud computing provides convenient access to reliable, high performance clusters and storage, without the need to purchase and maintain sophisticated hardware. For developers, virtualization allows scientific codes to be optimized and pre-installed on machine images, facilitating control over the computational environment. Preliminary tests are presented for serial and parallelized versions of the widely used x-ray spectroscopy and electronic structure code FEFF on the Amazon Elastic Compute Cloud, including CPU and network performance.
  01/2009;
• Source

  Available from: J. J. Rehr

  Article: Optical to UV spectra and birefringence of SiO_ {2} and TiO_ {2}: First-principles calculations with excitonic effects

  H. M. Lawler, J. J. Rehr, F. Vila, S. D. Dalosto, E. L. Shirley, Z. H. Levine
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  ABSTRACT: A first-principles approach is presented for calculations of optical, ultraviolet spectra including excitonic effects. The approach is based on Bethe-Salpeter equation calculations using the NBSE code combined with ground-state density-functional theory calculations from the electronic structure code ABINIT. Test calculations for bulk Si are presented, and the approach is illustrated with calculations of the optical spectra and birefringence of α-phase SiO2 and the rutile and anatase phases of TiO2. An interpretation of the strong birefringence in TiO2 is presented.
  Phys. Rev. B. 07/2008; 78(20).
• Article: Dynamic structure in supported Pt nanoclusters: Real-time density functional theory and x-ray spectroscopy simulations

  F. Vila, J. J. Rehr, J. Kas, R. G. Nuzzo, A. I. Frenkel
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  ABSTRACT: The nature of local atomic and electronic structure at the nanoscale is of both fundamental and technological importance. For example, supported metal nanoclusters exhibit a number of unusual phenomena including large structural disorder and bond-length contraction with increasing temperature. We investigate this behavior for a prototypical ten atom Pt cluster supported on γ alumina using temperature-dependent, real-time simulations based on density functional theory/molecular-dynamics and x-ray spectroscopy theory. The simulations reveal a complex dynamical structure on multiple-time scales including librational motion of the center of mass and fluctuating bonding characteristics, which explain many of the unusual properties.
  Phys. Rev. B. 78(12).