Theoretical Study On Structures Of Lanthanum At High Temperature And High Pressure

As we all know that lanthanum,cerium and praseodymium are all lanthanide metal elements and lanthanum is the first element of lanthanide metal.Its atomic number is 57 and contains 57 electrons.Under high pressure,it may have f orbital electrons.Lanthanum atomic mass is 138.09,so it may be difficult to calculate according to the primary principle.With the development of scientific technology,the awareness of the lanthanum metal is urgently needed.As so far,experimental and theoretical studies show that the lanthanum under low temperature and atmospheric pressure is dhcp phase structure.At a higher pressure,solid lanthanum transition from fcc phase to dfcc phase again.It also has a bcc phase at atmospheric 1000 K.Material generally exist four states in the nature.The four states are solid,liquid,gas,and plasma.Solid has been the focus in the study of condensed matter physics.After the liquid to liquid phase transition of cerium is discovered,liquid lanthanum research also obtain the extensive attention of the researchers.This article adopts particle swarm optimization methodology,as implemented in the CALYPSO code and combining with molecular dynamics simulation.We study the Lanthanide metal structure under high temperature and high pressure.1.Lanthanide metal has strong electronic interaction,the density functional theory describing lanthanide metal may have some shortcomings,so we test the potential of lanthanum.Under 30 GPa,we fit equation of state of lanthanum.At the same time,we simulate that the structure found by experiments and get the same phase sequence.At atmospheric pressure dhcp phase transition to fcc phase at 1.7GPa and dfcc phase 5.6GPa.At 100 GPa by structure prediction we get the fcc phase.It means that under low pressure the potential of vasp can be used to simulate and calculate the properties of lanthanum.2.On the basis of the information of lanthanum,We research lanthanum under high temperature and pressure by the first principles calculation and molecular dynamics simulation.The number of valence electrons of Lanthanum is 13 and atomic mass is 138.9055.Liquid with no periodic boundary conditions,simulation calculation requires very large cell including many atoms in order to eliminate the influence of the surfaces.We make an empirical potential Embedded Atom Method of lanthanum.3.In a recent literature reports that cerium has firs-order liquid to liquid phase transition,Lanthanum cerium are neighbors and there are one more f electron in cerium than Lanthanum.Lanthanum as the first element of lanthanide metal has the similar phase sequence and similar chemical properties with other lanthanide elements.We calculate the melting point of lanthanum under atmospheric pressure with different methods and discuss the differences among the different methods.