Structural, mechanical and vibrational study of uranyl silicate mineral soddyite by DFT calculations

Abstract

Uranyl silicate mineral soddyite, (UO2)2(SiO4)•2(H2O), is a fundamental component of the paragenetic sequence of secondary phases that arises from the weathering of uraninite ore deposits and corrosion of spent nuclear fuel. In this work, soddyite was studied by first principle calculations based on the density functional theory. As far as we know, this is the first time that soddyite structure is determined theoretically. The computed structure of

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

“…111,112 This pseudopotential includes scalar relativistic effects and has been used extensively in the research of uranyl containing materials. 88,[90][91][92][111][112][113][114][115][116][117] A single unit cell was used in the calculations. The initial guest to the unit cell of becquerelite was taken from Pagoaga et al 48 However, since the hydrogen atom positions were not determined in any of the previous experimental works, [47][48][49][50] the initial unit cell was supplemented by initial values of these positions and fully optimized.…”

“…In this case, there are no electrons in valence f orbitals and the use of the standard GGA approximation supplemented with empirical dispersion corrections has produced highly accurate results for the structural, spectroscopic, mechanic and thermodynamic properties of a large series of uranyl containing minerals as rutherfordine, soddyite, uranophane-a, studtite, metastudtite, g-UO 3 , dehydrated schoepite, schoepite and metaschoepite. 88,[90][91][92][111][112][113][114][115][116][117][104][105][106] It must be emphasized that the calculated thermodynamic properties of these materials were very accurate in those cases in which experimental values of these properties were available for comparison even at very low and high temperatures. [90][91][92]115,116 As an example, the errors in the computed enthalpies of formation of rutherfordine, 90 g-UO 3 , 90 and metaschoepite 92 at 700, 900, and 800 K were 1.6%, 1.0% and 2.0%, respectively.…”

Density Functional Theory Study of the Thermodynamic and Raman Vibrational Properties of γ-UO3 Polymorph

“…42 Theoretical methods may also be advantageous to determine these properties. [41][42][43][44] While theoretical solid state methods may be used in order to obtain these properties, the calculations required are very complex and expensive. [45][46] In this work, the equation of state of γ-UO3 is obtained and therefore the values of the bulk modulus and its derivatives are 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.…”