[lammps-users] Need your help for ibar parameter in MEAM potential in Lammps!!

Hi, dear LAMMPers and EAMers:

In command pair_style meam, it has 19 parameters: elt, lat, z, ielement, atwt, alpha, b0, b1, b2, b3, alat, esub, asub, t0, t1, t2, t3, rozero, ibar.
I know the meaning of all the parameters but last one ‘ibar’. It seems that it does not show up in MEAM potential formulas.

Could anyone give me help about this?

Best Regards


ibar determines the model of the background density that goes with the material that you are simulating.

This is the DYNAMO function for rhobar:

c this routine calculates unscaled rhobar
       function bar(rho0,A,ibar,z,dang1,dang2)
         implicit real*8 (a-h,o-z)
         data x0,n/-0.9,9/
c n=-x_0/(1+x_0)
c rhobar = rho0 * ang
c derivative of angular term wrt rho0 and A the angular density
         common /err/ ibarer,ibare
         data ibarer/0/
cprint *,'in bar ',rho0,A,ibar,z
         if(rho0.le.0.0) return
         if (ib.eq.0 .or. ib.eq.4) then
c ang = sqrt(1+A/rho0^2)
           ang = (1+A/rho0**2)
           if(ang.lt.1+x0) then
cprint *,'in bar ',rho0,A,x0
              dang1 = -A/(rho0**3*ang)
              dang2 = 1/(2*rho0**2*ang)
         elseif (ib.eq.1) then
c ang = exp(0.5 A/rho0^2)
           ang = exp(0.5*A/rho0**2)
           dang1 = -ang*A/rho0**3
           dang2 = ang/(2*rho0**2)
         elseif (ib.eq.2) then
c ang = exp(0.5 A/z^2)
           ang = exp(0.5*A/z**2)
           dang1 = 0
           dang2 = ang/(2.0*z**2)
         elseif (ib.eq.3) then
c ang = 2/(1+exp(-A/rho0^2)
           ang = 2.0/(1.0+ex)
           dang1 = -ang**2*ex*A/rho0**3
           dang2 = ang**2/2.0*ex/rho0**2
cprint *,'leaving bar',bar

There must be something analogous in LAMMPS.

Steve Valone