[Wien] Suggestions on Size of SuperCell for phonon Calculations

[Ghosh SUDDHASATTWA]

Dear Wien2k users, 

I have an orthorhombic structure with the following lattice parameters which
is pasted form the d45 file 

# LATTICE

Base-centered (C) Orthorhom

# Lattice Vectors C of Crystallographic Unit Cell:

        2.8124312897     0.0000000000     0.0000000000

        0.0000000000     5.7835172524     0.0000000000

        0.0000000000     0.0000000000     5.1025574719

# Lattice Vectors of Primitive Unit Cell:

        1.4062156448     1.4062156448     0.0000000000

       -2.8917586262     2.8917586262     0.0000000000

        0.0000000000     0.0000000000     5.1025574719

#Supercell Transformation Matrix L; S=CL

        4.0000000000     0.0000000000     0.0000000000

        0.0000000000     2.0000000000     0.0000000000

        0.0000000000     0.0000000000     2.0000000000

 

The case is with only one atom and a 64 atom supercell  is taken with 1400
k-points in the FBZ

Now, when I do 

grep -e:FGL case_1.scf, I get the following 

:FGL054:  54.ATOM                -0.144000000   -34.520000000
-0.244000000 pa

rtial forces

:FGL055:  55.ATOM                -0.044000000   -34.526000000
-0.033000000 pa

rtial forces

:FGL056:  56.ATOM                -0.081000000   -34.515000000
-0.020000000 pa

rtial forces

:FGL057:  57.ATOM                 0.029000000   -34.731000000
-0.310000000 pa

rtial forces

:FGL058:  58.ATOM                -0.143000000   -34.607000000
-0.035000000 pa

rtial forces

:FGL059:  59.ATOM                -0.067000000   -34.663000000
-0.001000000 pa

rtial forces

:FGL060:  60.ATOM                -0.027000000   -34.491000000
-0.032000000 pa

rtial forces

:FGL061:  61.ATOM                 0.025000000   -34.312000000
0.281000000 pa

rtial forces

:FGL062:  62.ATOM                -0.160000000   -34.698000000
0.182000000 pa

rtial forces

:FGL063:  63.ATOM                 0.051000000   -34.553000000
-0.024000000 pa

rtial forces

:FGL064:  64.ATOM                 0.011000000   -34.484000000
0.185000000 pa

rtial forces

 

It has a significant force in the y-direction. Can anybody suggest what
should be the size of the supercell now?  64 atom supercell seems 

To be very large, still the forces are not pretty good in the y-dir.

Can anybody help me in this regard

 

Thanks 

SG 

 

 

 

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