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Manuscript Title: OptaDOS: A Tool for Obtaining Density of States, Core-level and Optical Spectra from Electronic Structure Codes
Authors: Andrew J. Morris, Rebecca J. Nicholls, Chris J. Pickard, Jonathan R. Yates
Program title: OptaDOS
Catalogue identifier: AESK_v1_0
Distribution format: tar.gz
Journal reference: Comput. Phys. Commun. 185(2014)1477
Programming language: Fortran 95.
Computer: Any architecture with a Fortran 95 compiler.
Operating system: Linux, Mac OS X.
Has the code been vectorised or parallelized?: Yes, using MPI
RAM: 10 Mb
Word size: 32 or 64
Keywords: Electronic structure, Density-functional theory, Density of States, EELS, Optical spectra.
PACS: 31.15.E-, 79.20.Uv.
Classification: 7.2, 7.3.

External routines: MPI to run in parallel, CASTEP

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 broadening. This increases the resolution of the predicted spectra.

Unusual features:
Simple and user-friendly input system. Along with the usual band energies, band gradients are used to generate the linear extrapolation and adaptive broadening schemes producing a superior output able to represent both dispersive and localised bands concurrently.

Additional comments:
The input data to OptaDOS are single-particle eigenenergies and dipole transition coefficients. OptaDOS has an interface to obtain these from the CASTEP plane wave density-functional theory (DFT) code. The interfacing of OptaDOS with other electonic structure codes, which are also capable of generating such inputs, is currently being undertaken

Running time:
A few seconds to ~10 minutes.