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Manuscript Title: turboEELS - A code for the simulation of the electron energy loss and inelastic X-ray scattering spectra using the Liouville-Lanczos approach to time-dependent density-functional perturbation theory
Authors: Iurii Timrov, Nathalie Vast, Ralph Gebauer, Stefano Baroni
Program title: turboEELS
Catalogue identifier: AEXB_v1_0
Distribution format: tar.gz
Journal reference: Comput. Phys. Commun. 196(2015)460
Programming language: Fortran 95.
Computer: Any computer architecture.
Operating system: GNU/Linux, AIX, IRIX, Mac OS X, and other UNIX-like OS's.
Keywords: Electron energy loss spectroscopy, Inelastic X-ray scattering, Time-dependent density functional perturbation theory, Quantum ESPRESSO, Linear response, Liouville-Lanczos approach.
PACS: 31.15.ee, 71.45.Gm, 78.70.-g, 79.20.Uv.
Classification: 7.2.

External routines: turboEELS is a tightly integrated component of the Quantum ESPRESSO distribution and requires the standard libraries linked by it: BLAS, LAPACK, FFTW, MPI.

Nature of problem:
Calculation of the electron energy loss and inelastic X-ray scattering spectra of periodic solids.

Solution method:
The charge-density susceptibility of a periodic system is expressed in terms of the resolvent of its Liouvillian superoperator within time-dependent density functional perturbation theory. It is calculated using non-Hermitian or pseudo-Hermitian variants of the Lanczos recursion scheme, whose implementation does not require the calculation of any virtual states. Pseudopotentials (both norm-conserving and ultrasoft) are used in conjunction with plane-wave basis sets and periodic boundary conditions. Relativistic effects (spin-orbit coupling) can be included in calculations.

Linear-response regime. Adiabatic exchange-correlation kernels only. No hybrid functionals. Collinear spin-polarized formalism is not supported, only non-collinear spin-polarized case can be used. Spin-orbit coupling cannot be used with ultrasoft pseudopotentials. No magnetism. No Hubbard U formalism. No PAW pseu- dopotentials.

Unusual features:
No virtual orbitals are used, nor even calculated. A single Lanczos recursion gives access to the whole spectrum at fixed transferred momentum.

Additional comments:
The distribution file of this program can be downloaded from the Quantum ESPRESSO website: http://www.quantum-espresso.org/, and the development version of this program can be downloaded via SVN from the QE-forge website: http://qe-forge.org/gf/project/q-e/.

Running time:
From a few minutes for elemental bulk systems with a few atoms in the primitive unit cell on serial machines up to many hours on multiple processors for complex systems (e.g., surfaces with high Miller indices) with dozens or hundreds of atoms.