Determination of quadrupole moment and isomeric shift for 119Sn. Comparison of different methods based on DFT calculations

H.K. NARRO; C. CASTÓN BRUSASCO; L.A. ERRICO; A.V. GIL REBAZA

La Plata

Workshop; X Workshop on Novel Methods for Electronic Structure Calculations; 2023

Hyperfine techniques in general, and Mossbauer spectroscopy(MS) in particular, have been ex-tensively employed for the structural, electronic, and magnetic characterization of materials. Whatmakes these techniques particularly interesting is their ability to measure properties related to chem-ical state, charge symmetry (the electric field gradient tensor, EFG), and spin polarization andcurrents (hyperfine magnetic fields, BHF) at the site of a core probe. In the case of EM, one of theisotopes of Fe (57Fe) and Sn (119Sn) are the most commonly employed probes, making this techniqueparticularly suitable for studying a very broad set of materials of both basic and applied interest. Theuse of MS allows information related to the electronic and magnetic configuration at the core-probesite and its immediate surroundings to be obtained on a nanoscopic scale. The experiment-theorycombination allows us to extract all the information contained in the experimental results. To achievethis, different structural and electronic scenarios will beproposed for the system under study, andfrom the theory-experiment comparison, it will be determined which one best reproduces the exper-iments.In particular, three hyperfine parameters are determined via MS: the isomeric shift (IS), the quadrupolesplitting (QS), and the hyperfine field (BHF). In this paper, we focus on the first two. The IS is anobservable that provides information about the local chemical bonding of the probe- atom, and theQS is a fingerprint of the charge symmetry around the probe nucleus. The information containedin these parameters is the product of a nuclear quantity (specific to the core- probe) and one thatdepends on the crystalline environment where the probe is located. In the case of IS, the nuclear pa-rameter is the constantα(which depends on the nuclear radii involved in the Mossbauer transition),and the material property is the electron density at the coresite (obtained from DFT calculations).In the case of QS, the nuclear property is the quadrupole momentum Q, and the electronic propertyis the GCE (obtained from the DFT calculation). It is clear then that a precise and accurate knowl-edge of and Q is fundamental to be able to translate; from calculated to experimentally determinedquantities and thus to compare theory with experiment.In the present work, a wide variety of Sn-based compounds have been considered to calculate theGCE and electron density at the probe core site in order to correlate the results obtained by DFTwith the experimental values, thus allowing and Q to be obtained. The Full Potential AugmentedPlane Waves (FP-LAPW) method, which is a well-established method for electronic structure cal-culations, and the Gauge-Including Projected Augmented Waves (GIPAW) method implemented in the Quantum Espresso plane+pseudopotential wave code was used for the calculations, in order toestablish the capability of this method for the calculationof hyperfine properties. In the case of IS,calculations were also performed using the full-potentiallocal-orbital (FPLO) method, which, unlikeFP-LAPW, does not use the point core hypothesis.