Dysurf: A program for simulating four-dimensional dynamical structure factor

A Fortran program that can be applied to simulate the four-dimensional dynamical structure factors (Dysurf) for inelastic neutron and inelastic X-ray scattering experiments is presented. With the underlying theoretical formalism, the detailed implementation of the program is described. Based on the second-order force constants from the first-principles method, the Dysurf code can well reproduce the measured spectroscopies of those scattering experiments. Four main applications of this code with the corresponding examples are introduced here, including the multi-dimensional dynamical structure factors, thermal diffuse scattering, line cut at specific points in the Brillouin zone and sample design. This program will be helpful in terms of designing and explaining related inelastic scattering experiments. PROGRAM SUMMARY Program Title: Dysurf CPC Library link to program files: https://doi.org/10.17632/gx6m63svjy.1 Developer's repository link: https://github.com/Dysurf/Dysurf Licensing provisions: GNU General Public License version 3.0 Programming language: Fortran External routines/libraries: LAPACK Nature of problem: Inelastic neutron or inelastic X-ray scattering to measure phonon properties is a complex experiment, in which the single crystal sample alignment, scattering geometry, dispersion identification, and data processing are all time-consuming to experimentalists. Given the limited beamtime approved, experimentalists hope to obtain the high-quality data the greatest extent during the measurements. Thus, an efficient and time-saving method is desired. Theoretical spectroscopy is a very powerful tool in comparing and explaining the inelastic scattering data, although its utilization is rarely reported to help the scattering measurements so far. Developing reliable and sophisticated simulations to explore those applications corresponding to phonon measurements is very promising to facilitate experiment design and improve the inelastic scattering measurements, e.g., predetermining sample parameters and saving beamtime. The simulated spectroscopies can also be complementary to experimental measurements in terms of analyzing and illustrating results. Solution method: Based on the second-order force constants from density functional theory, the four-dimensional dynamical structure factors from inelastic neutron and X-ray scattering measurements can be well predicted, with experimental conditions, scattering geometries, and instrument resolution functions properly considered.