XSpectra: a density-functional-theory-based plane-wave pseudopotential code for XANES calculation

The XSpectra code calculates XANES spectra at the K, L1 and L2,3 edges, including both electric dipole and quadrupole transitions. Density-functional theory and the Born–Oppenheimer approximation are used. The implementation relies on plane-wave basis sets, pseudopotentials and periodic boundary conditions. XSpectra belongs to the Quantum ESPRESSO distribution, an integrated suite of open-source computer codes for electronic structure calculations. XSpectra reads the self-consistent charge density produced by the PWscf code of the Quantum ESPRESSO distribution and acts as a post-processing tool. Core-hole effects are included by considering a supercell containing one absorbing atom, the pseudopotential of which is generated with a core hole in the appropriate core level. The all-electron final state wavefunctions are constructed using the projector augmented-wave method. The XANES cross section is calculated using the Lanczos method and a continued fraction expansion, avoiding the explicit calculation of empty states. The capabilities of the code are illustrated via selected examples.