Core effects on the energetics of solid Li at high pressure

Using the recently proposed P4(1)32 structure as a test case, the accuracy of three three-electron Li pseudopotentials for plane-wave electronic structure calculations at very high pressure was examined. At high Li density (r(s)< 1.94), it is found that carefully chosen core radii cutoffs in the construction of the pseudopotential are necessary in order to reproduce results obtained from all-electron full potential linearized augmented plane-wave method at very high pressure. This accuracy is needed to resolve small enthalpy differences between competitive polymorph phases in this pressure range. In this manner, a three-electron pseudopotential in the Troullier-Martins form was constructed. Using this pseudopotential, it is found that a previously proposed dimer Cmca-8 structure is slightly more stable than the Cmca-24 structure at pressure higher than 456 GPa. The P4(1)32 structure is found having higher enthalpy than both Cmca-8 and Cmca-24 structures up to at least 500 GPa.