Publications using the Wurm project data

The main publication describing the WURM project.

The WURM project—a freely available web-based repository of computed physical data for minerals
Razvan Caracas and Ema Bobocioiu

The WURM project is a database of computed Raman and infrared spectra and other physical properties for minerals. The calculations are performed within the framework of the density-functional theory and the density-functional perturbation theory. The database is freely available for teaching and research purposes and is presented in a web-based format, hosted on the web site. It provides the crystal structure, the parameters of the calculations, the dielectric properties, the Raman spectra with both peak positions and intensities and the infrared spectra with peak positions for minerals. It shows the atomic displacement patterns for all the zone-center vibrational modes and the associated Raman tensors. The web presentation is user friendly and highly oriented toward the end user, with a strong educational component in mind. A set of visualization tools ensures the observation of the crystal structure, the vibrational pattern, and the different spectra. Further developments include elastic and optical properties of minerals.

please cite as: R. Caracas, E. Bobocioiu, American Mineralogist, The WURM project – a freely available web-based repository of computed physical data for minerals, 96, 437–443, (2011).

Theoretical modelling of Raman spectra
Razvan Caracas and Ema Bobocioiu

The atomic lattices are not static ensemble of atoms, but rather the atomic nuclei in solids are always vibrating. Various factors like temperature, external electric or magnetic fields, pressure, etc. can affect these vibrations. The pattern of vibrations is structural- and compound-dependent. Consequently one of its possible uses is determinative, as recorded in Raman and/or infrared spectra. Here we briefly present the theoretical basis of lattice dynamics in the density-functional perturbation theory formalism. Then we discuss in detail the formalism used to compute the Raman spectra, with both peak position and intensity. We exemplify with the WURM project, a web-based freely available repository of computed physical properties for minerals, focused around the Raman spectra.

please cite as: Theoretical modeling of Raman spectra R. Caracas and E. Bobocioiu in Raman Spectroscopy Applied to Earth Sciences and Cultural Heritage EMU Notes in Mineralogy volume 12, Eds. J. Dubessy, M.-C. Caumon, F. Rull. Publisher: EMU (2012)

Anharmonicity of graphite from UV Raman spectroscopy to 2700 K
G. Montagnac, R. Caracas, E. Bobocioiu, F. Vittoz, B. Reynard

WURM contribution: We compute the Raman spectra of graphite with varying a and c values to mimic the effect of temperature. We compare the results of calculations with experiments are eventually we able to estimate anharmonicity.
First-order Raman spectra of pyrolytic graphite (PG) and highly oriented pyrolytic graphite (HOPG) were recorded in situ up to 2670 K and 2491 K, respectively, using a development of wire-loop heating cell technique attached to a UV-Raman spectrometer (244 nm). Raman shift of the E2g in-plane stretching mode of graphite (G band) is used to discuss the anharmonicity by a comparison with calculations in the density-functional theory (DFT). High temperature Raman shifts are well described by anharmonic DFT calculations [1] up to 900 K. Anharmonicity is also determined from the temperature dependence of the Raman linewidth. The quartic term of phonon-phonon scattering process dominates at high temperature with respect to electron-phonon coupling that causes a slight decrease of linewidth with increasing temperature below 1000 K. The G band position is determined with a good reproducibility to 2700 K and can be used as a thermometer for in situ studies. Deep UV-Raman proves a viable solution for expanding signi cantly the temperature range for studying in situ vibrational properties of condensed matter, and particularly the monitoring of carbon-based material processing.

please cite as: G. Montagnac, R. Caracas, E. Bobocioiu, F. Vittoz, and B.Reynard, Anharmonicity of graphite at high temperature, Carbon, 54, 68-75 (2013).

Raman spectroscopic properties and Raman identification of CaS-MgS-MnS-FeS-Cr2FeS4 sulfides in meteorites and reduced sulfur-rich systems
Caroline Avril, Valérie Malavergne, Razvan Caracas, Brigitte Zanda, Bruno Reynard, Emeline Charon, Ema Bobocioiu, Fabrice Brunet, Stephan Borensztajn, Sylvain Pont, Martine Tarrida and François Guyot

WURM contribution: We use first-principles calculations to bring some light on first-ever Raman measurements on a series of sulfide minerals present in meteorites.
Raman spectra were acquired on a series of natural and synthetic sulfide minerals, commonly found in enstatite meteorites: oldhamite (CaS), niningerite or keilite ((Mg,Fe)S), alabandite (MnS), troilite (FeS), and daubreelite (Cr2FeS4). Natural samples come from three enstatite chondrites, three aubrites, and one anomalous ungrouped enstatite meteorite. Synthetic samples range from pure endmembers (CaS, FeS, MgS) to complex solid solutions (Fe, Mg, Ca)S. The main Raman peaks are localized at 225, 285, 360, and 470 cm−1 for the Mg-rich sulfides; at 185, 205, and 285 cm−1 for the Ca-rich sulfides; at 250, 370, and 580 cm−1 for the Mn-rich sulfides; at 255, 290, and 365 cm−1 for the Cr-rich sulfides; and at 290 and 335 cm−1 for troilite with, occasionally, an extra peak at 240 cm−1. A peak at 160 cm−1 is present in all Raman spectra and cannot be used to discriminate between the different sulfide compositions. According to group theory, none of the cubic monosulfides oldhamite, niningerite, or alabandite should present first-order Raman spectra because of their ideal rocksalt structure. The occurrence of broad Raman peaks is tentatively explained by local breaking of symmetry rules. Measurements compare well with the infrared frequencies calculated from first-principles calculations. Raman spectra arise from activation of certain vibrational modes due to clustering in the solid solutions or to coupling with electronic transitions in semiconductor sulfides.

please cite as: Avril, C., Malavergne, V., Caracas, R., Zanda, B., Reynard, B., Charon, E., Bobocioiu, E., Brunet, F., Borensztajn, S., Pont, S., Tarrida, M. and Guyot, F. (2013), Raman spectroscopic properties and Raman identification of CaS-MgS-MnS-FeS-Cr2FeS4 sulfides in meteorites and reduced sulfur-rich systems. Meteoritics & Planetary Science, 48: 1415–1426. doi: 10.1111/maps.12145