The ABINIT Users Mailing List ( CLOSED )

[David Clatterbuck <clatterbuck1@llnl.gov>]

Fellow Abinitioners,

It is my understanding that in most cases LDA will "overbind" compared to 
experiment, causing the lattice parameter to be too small and the bulk 
modulus too big.

In trying out different pseudopotentials for several different problems, 
I've begun to notice a pattern that the Troulier-Martins pseudopotentials 
available on the Abinit website (the ones generated by A. Khein and D.C. 
Allan) tend to produce lattice parameters that are bigger than experiment 
as well as bulk moduli that are bigger than experiment. With the HGH 
pseudopotentials, I tend to get the expected LDA overbinding (lattice 
parameters too small, bulk moduli too big). Most of my work in this area 
has been on on metals (Al, Cu, Ta, Mo, W, ....). All of the calculations 
have been thoroughly tested for convergence (ecut, ngkpt, tsmear, nband).

Has anyone else noticed this? Any ideas as to why there is this systematic 
difference between the two types of pseudopotentials? Is it related to the 
fact that the TM pseudopotentials tend to be softer (lower ecut necessary 
to converge)? Based on this, is the error between 
all-electron-full-potential LDA calculations and pseudopotential LDA 
calculations larger for the case of TM pseudopotentials?

Thanks for any thoughts,

David Clatterbuck
Postdoctoral Researcher
Lawrence Livermore National Lab