OptaDOS: A tool for obtaining density of states, core-level and optical spectra from electronic structure codes

We present OptaDOS, 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 show produces higher accuracy spectra than standard fixed-width Gaussian broadening. OptaDOS may be straightforwardly interfaced to any electronic structure code. OptaDOS is freely available under the GNU General Public licence from http://www.optados.org. Program title:OptaDOS Catalogue identifier: AESK_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AESK_v1_0.html Program obtainable from: CPC Program Library, Queen’s University, Belfast, N. Ireland Licencing provisions: GNU General Public License, version 3 No. of lines in distributed program, including test data, etc.: 110299 No. of bytes in distributed program, including test data, etc.: 1889705 Distribution format: tar.gz Programming language: Fortran 95. Computer: Any architecture with a Fortran 95 compiler. Operating system: Linux, Mac OS X. Has the code been vectorised or parallelised?: Yes, using MPI RAM: 10 MB Word size: 32 or 64 Classification: 7.2, 7.3. External routines: MPI to run in parallel, CASTEP or any other electronic structure code capable of generating single-point eigenenergies and dipole transition coefficients. Nature of problem: Many properties of materials can be described using integration over the Brillouin zone such as core-level and low-loss EELS and optical spectra. This integration is performed computationally using a grid of k-points. The discrete energy eigenvalues must be interpolated into a continuous spectra. The most common method broadens the eigenvalues using a Gaussian function. Gaussian broadening suffers from slow convergence with number of k-points and a difficulty in resolving fine spectral features. Solution method: OptaDOS improves the underlying Brillouin zone integration beyond fixed-width Gaussian broadening by using band gradients to perform adaptive and linearly extrapolated