OptaDOS

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{{#if: Andrew J. Morris, University of Cambridge, Cambridge, UK
Rebecca J. Nicholls, University of Oxford , Oxford, UK
Chris J. Pickard, University College London , London, UK

Jonathan R. Yates, University of Oxford , Oxford, UK
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Source authors:
Andrew J. Morris, University of Cambridge, Cambridge, UK
Rebecca J. Nicholls, University of Oxford , Oxford, UK
Chris J. Pickard, University College London , London, UK
Jonathan R. Yates, University of Oxford , Oxford, UK

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License: GPL v3

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Download: Project page

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OptaDOS is a program for calculating core-electron and low-loss electron energy loss spectra (EELS) and optical spectra along with total-, projected- and joint-density of electronic states (DOS) from single-particle eigenenergies and dipole transition coefficients.

Energy-loss spectroscopy is an important tool for probing bonding within a material. Interpreting these spectra can be aided by first principles calculations. The spectra are generated from the eigenenergies through integration over the Brillouin zone. An important feature of this code is that this integration is performed using a choice of adaptive or linear extrapolation broadening methods which we have shown produces higher accuracy spectra than standard fixed-width Gaussian broadening. OptaDOS currently interfaces out-of-the-box with CASTEP and ONETEP and may be straightforwardly interfaced to any electronic structure code.

Algorithm

Extrapolating from each k-point rather than interpolating between adjacent points eliminates the band-crossing problem. Müller and Wilkins show that for free electron bands the DOS is a smooth parabola when using the extrapolative method and a rough unconverged spectrum with the interpolative approach when using the same k-point mesh [1].

The linear extrapolative scheme still does not represent van Hove singularities as well as a second-order approach. Band curvatures may be combined with Löwdin perturbation theory to extrapolate to higher order [2] and [3]. Linear extrapolative broadening may be chosen for OptaDOS calculations with, broadening : linear.

An approximation to linear extrapolation method was proposed by Yates et al. [4]. Each sub-cell’s contribution to the DOS is broadened by a Gaussian function whose width, ω, is proportional to the energy band gradient as its k-point. This simple approach removes the spurious oscillations of the fixed broadening whilst maintaining the sharper features. The adaptive broadening scheme was introduced in Ref. [4] in the context of Wannier interpolation of BZ quantities. However, the scheme is more general that this, and with OptaDOS we apply adaptive broadening directly to the quantities obtained from the electronic structure calculation. Adaptive extrapolative broadening may be chosen for OptaDOS calculations with, broadening : adaptive .

Programming interface

Can be found in user guide (Appendix A).

Or contact the OptaDOS mailing list OPTADOS@JISCMAIL.AC.UK.

Software description and installation

The latest tarball of the distribution is available from here.

Prerequisites

  • Fortran95 compiler
  • MPI libraries (if parallel execution is required).
  • An electronic structure code able to generate Kohn-Sham eigenstates, (or at least the code's outputs).
  • For partial density of states calculations, the density projected onto local orbitals is also required.
  • For linear and adaptive broadening, and optical calculations, the optical matrix elements are also required.

Instructions

OptaDOS is usually obtained in a gzipped tarball, optados-X.X.tar.gz. Extract this

tar -xzf optados-X.X.tar.gz

in the desired directory. Inside the top level optados/ directory are a number of subdirectories, documents/, examples/. The code may be compiled using the Makefile in the optados/ directory. The SYSTEM, BUILD, COMMS_ARCH and PREFIX flags must be set, either in the make.system, or from the command line (for example:

make BUILD=fast

No external libraries are required for serial execution.

  • SYSTEM: Choose which compiler to use to make OptaDOS. The valid values are: g95 (default), gfortran, ifort, nag, pathscale, pgf90 and sun. Other compilers may be added manually by editing the make.system file.
  • BUILD: Choose the level of optimisations required when making OptaDOS. The valid values are: fast (default): all optimisations or debug: no optimisations. All compiler warnings. Makes a binary containing full debugging information in operating system’s native format, including information suitable for analysing using the gprof profiler.
  • COMMS_ARCH: Whether to compile for serial or parallel execution. The valid values are: serial (default) or mpi.
  • PREFIX: Choose where to place the OptaDOS binary. The default is the OptaDOS directory.

Publications

The main paper describing this software can be found in these references [5],[6] .

References

  1. J.E. Müller, J.W. Wilkins, Phys. Rev. B, 8, 4331 (1984). DOI: 10.1103/PhysRevB.29.4331
  2. C.J. Pickard, M.C. Payne, Phys. Rev. B, 59, 7, 4685, (1999), DOI: 10.1103/PhysRevB.59.4685
  3. C.J. Pickard, M.C. Payne, Phys. Rev. B, 62, 7, 4383 (2000), DOI: 10.1103/PhysRevB.62.4383
  4. 4.0 4.1 J.R. Yates, X. Wang, D. Vanderbilt, I. Souza, Phys. Rev. B, 75, 195121 (2007), DOI: 10.1103/PhysRevB.75.195121
  5. Andrew J. Morris, R. J. Nicholls, C. J. Pickard and Jonathan R. Yates, OptaDOS: A tool for obtaining density of states, core-level and optical spectra from electronic structure codes, Computer Physics Communications 5, 1477 (2014). DOI: 0.1016/j.cpc.2014.02.013
  6. R. J. Nicholls, Andrew J. Morris, , C. J. Pickard and Jonathan R. Yates, OptaDOS - a new tool for EELS calculations, J. Phys.: Conf. Ser. 371, 012062 (2012). DOI: 10.1088/1742-6596/371/1/012062