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[Linhui Ye <yelinhui1@yahoo.com>]

I've solved the problem. All is because of that the
calculation only performed 5 broyden steps. It is not
enough to converge the stress.

Setting ntime to 80, the final stress became
neglectible small.

Linhui

--- Linhui Ye <yelinhui1@yahoo.com> wrote:
> Dear abinit users,
> 
> I'm using abinit to calculate the lattice parameters
> of hexagonal garphite. The 3 unit vectors are to be
> relaxed(optcell=2 and ionmov=2). I have the
> following
> questions:
> 
> 1. The convergence parameters for cell relaxation,
> are
> toldmxf and strfact, right? In cell relaxation, the
> modification of any one of the two parameters is
> sufficient to define a convergence criterion, right?
> 
> 2. If I set strfact=1d-4 and toldmxf=1d-8, are these
> resonable values? Is this equivalent to strfact=1d-2
> and toldmxf=1d-10?
> 
> 3. The output shows(only diagonal element shown
> here):
>   sigma(1 1)= -1.66117688E-05  (Hartree/Bohr^3)
>   sigma(2 2)= -1.66117688E-05  
>   sigma(3 3)=  5.92238033E-06  
> - sigma(1 1)= -4.88735015E-01  (GPa)
> - sigma(2 2)= -4.88735015E-01  
> - sigma(3 3)=  1.74242410E-01  
>   [Pressure=  2.6774E-01 GPa]
> 
> showing the "residue pressure" is about 0.27 GPa,
> right?How good is this calculation w.r.t. the
> residue
> pressure? What is the relation between
> [Pressure=xxx]
> and the - sigma(xx) values?
> 
> 4. I tried to further eliminate the residue
> pressure,
> by increasing strfact to larger value, or decreasing
> toldmxf to smaller value, but the residue pressure
> seems to change little. Why?
> 
> 5. The cell relaxation seems to be sensitive to the
> input trail lattice parameter. If I use in input
> file
> (a=2.44, c=6.50) or (a=2.46,c=6.70), the final
> lattice
> parameters converge to (a=2.441,c=6.63) and
> (a=2.449,c=6.68), respectively. The differences
> seems
> to be too large. Why are the final values sensitive
> to
> input trail values?
> 
> 6. Generally, how good is cell relaxation?
> 
> 7. The last question is concerning with the FHI98PP
> pseudopotential. Here the potential can be generated
> in Harmann type, or Troulier-Martin type. For any
> element, do these 2 types of pseudopotential vary in
> accuracy? Or they do have same accuracy? Is it true
> that in abinit only the Troulier-Martin type
> pseudopotentials may be used?
> 
> Thank you for reading this.
> 
> Linhui
> 
> 
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