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In this study, using the density functional theory, the mechanical properties of methylammonium lead halide perovskites (CH3NH3PbX3, X = I, Br, Cl) were investigated. Young’s modulus, bulk modulus, and shear modulus, Poisson’s ratio, and many other parameters were calculated using the PBEsol and vdW approximations. Also, in this work, utilizing a new accuracy in calculating the elastic constants, the intense conflict between the previous theoretical results and the experimental data were fixed. Moreover, for the first time, through combination of the PBEsol and vdW methods, the effect of the interaction between methylammonium and PbX3 scaffold on the mechanical properties of lead halide perovskites was well cleared. In continuation, using the PBEsol+vdW method, a phase transition appeared for the MAPbBr3 and MAPbCl3 structures, which proved more stability of MAPbBr3 and MAPbCl3 in comparison with MAPbI3. In what follows, by studying these materials under an applied strain beyond the harmonic region, the transition zone to the plastic area in the strain region of 5.5% and smaller was identified, and the small values of the aforementioned applied strains were found to be the reason for the instability of these materials at room temperature and above.

 

Ref: https://pubs.acs.org/doi/abs/10.1021/acs.jpcc.7b07129

 

 

 

 

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In the current work, mechanical properties of SiC graphene sheet and influence of temperature on those properties are studied. The purpose of this work is to investigate the temperature dependency of the Young’s modulus and Bulk’s modulus of SiC graphene sheet. To reach these goals, density functional theory (DFT) and quasi-harmonic approximation (QHA) methods are used to calculate energies of electrons and phonons, and consequently to obtain total energy of system. Results have been compared with existing data from literature and good agreement has been found. It is found that the effect of temperature on the mechanical properties of the SiC graphene sheet is significant.

 

Ref: https://www.sciencedirect.com/science/article/pii/S003810981500407X

 

 

 

 

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