Becquerelite mineral phase: crystal structure and thermodynamic and mechanical stability by using periodic DFT

Abstract

The full crystal structure of becquerelite mineral phase was successfully determined using theoretical solid-state methods for the first time. Additionally, a complete study of its thermodynamic and mechanical properties and stability is reported.

Silver Oxalate: Mechanical Properties and Extreme Negative Mechanical Phenomena

“…[77] The calculated elasticity matrix, C i j , is reported in Table S5, Supporting Information. As in previous studies, [1,2,5,6,[83][84][85][86] the Reuss approximation was chosen as the best approach in the case of silver oxalate because it provided the best comparison of the results for the calculated bulk modulus, B = 9.64 ± 2.51 GPa, with that determined from the EOS. For monoclinic crystals, the generic necessary and sufficient Born criterion is that all eigenvalues of the C matrix be positive.…”

“…The mechanical properties of polycrystalline silver oxalate were determined using the Voigt, [80] Reuss, [81] and Hill [82] schemes. As in previous studies, [1,2,5,6,[83][84][85][86] the Reuss approximation was chosen as the best approach in the case of silver oxalate because it provided the best comparison of the results for the calculated bulk modulus, B = 9.64 ± 2.51 GPa, with that determined from the EOS. The results are reported in Table 1.…”

Revealing hydrogen atoms in a highly-absorbing material: an X-ray diffraction study and Torque method calculations for lead-uranyl-oxide mineral curite

“…Therefore, the combination of methods, usually comprising XRD structure determination and with the parameter from Density Functional Theory (DFT) optimization of crystal structure, has become to be used more widely. [24][25][26] The current study demonstrates the possibility of elucidation H atoms in the structure of highly-absorbing material for Xrays, where the localization of hydrogens remains poorly constraint. Here, we demonstrate the successful hydrogen atom localization by combining X-ray diffraction and a recently developed Torque method.…”

Periodic density functional theory study of the Raman spectrum of the hydrated uranyl oxyhydroxide mineral becquerelite

“…The development of a new high-quality norm conserving relativistic pseudopotential specific for uranium atom [27][28], has allowed an accurate theoretical solid-state treatment of these materials [29][30]. These theoretical studies have been used not only as a complement of the experimental techniques allowing the determination of the complete crystal structures of many uranyl containing materials [31][32][33] and the precise assignment of their Raman spectra [26,28,31,[34][35], but also as a very powerful predictive tool of their thermodynamic, mechanical and optical properties [31][32][33][34][35][36][37][38][39][40][41][42][43][44].…”

“…The computations were carried out by using Periodic Density Functional Theory with plane waves and pseudopotentials [50]. The theoretical determination of this Raman spectrum was possible due to the development of the high-quality pseudopotential specific for the uranium atom [27][28] mentioned in previous paragraphs and also to the recent optimization of the full crystal structure of this mineral [32] including the position of all hydrogen atoms in the corresponding unit cell. Since the determination of the hydrogen atom positions was not possible by structure refinement of the X-ray diffraction data in previous experimental works [51][52][53][54], they were fully optimized using theoretical methods [32].…”