First Principles Calculations Of The Structural,Electronic,Elastic And Thermodynamic Properties Of Uranium

We analyze physical properties of ?,?,and ? uranium using the first-principles method,which is one of the most popular research topics based on the density functional theory.Actinide elements and their compounds exhibit many fascinating physical behaviors and play special role in nuclear applications,because of complex electronic structure and strong correlation of the f electron.As a member of the actinides to accommodate a 5f electron,it requires a good understanding on properties of uranium under different environmental conditions.Specific details can be divided into three parts:Firstly,we introduce the research background,literature review the significance,and research methods of this study.Secondly,the optimized structural parameters,atomic volume under pressures from 0 to 100 GPa as well as the value of bulk modulus from state equation fitting and its pressure derivative at ambient condition are calculated by using the projector augmented wave(PAW)method.The density of states(DOS)has been determined in order to analyze variance in electronic structure between the ?,? and ? phases under high pressure up to 100 GPa.Furthermore,the effects of pressure on elastic constants,bulk modulus,shear modulus,Young's modulus,Poisson's ratio,elastic wave velocities,and Debye temperature of ?-U are investigated,and we notice that Cmcm-U should be stabilized mechanically at least up to100 GPa.Experimental investigation of ? and ? phases of uranium is quite difficult due to the low temperature mechanical instability of the crystal structure,we only investigate the mechanical properties in ground state.It is mechanically stable in the ground state for ?-U,because elastic constants satisfy the mechanically stable criteria of tetragonal structure.For ?-U,it is mechanically unstable due to the fact that its elastic constants unsatisfy the mechanically stable criteria of cubic structure.Last,we report on thermodynamic properties of ?,bct,and ?uranium metal within the framework of quasi-harmonic Debye model.We have calculated the total energy as a function of atomic volume,and one can clearly see that the ?-U is more stable than other structure.Furthermore,the theoretical results about the pressure and temperature dependence of the volume,heat capacity,entropy of ?-U show good agreement with the previous theoretical and experimental results.This is the first theoretical prediction about the temperature dependence of the thermodynamic properties of bct and ?-U.