[Pw_forum] vc-relax with diverging SCF error

[Christopher O'Brien]

PWSCF users:
I have been struggling for quite some time to perform a vc-relax calculation on a simple system of 96 Cu atoms. I am confident that the input is correct as an ion relaxation run converges in one scf cycle to a pressure of -11.54 kbar with the same parameters as the vc-relax calculation (shown below). 

As seen in the output file, the problem with the vc-relax calculation is that the SCF error will increase with each iteration. I have tried to remedy this issue by restricting the maximum movement distance of both the cell and ions to no avail. Unfortunately, I cannot turn on symmetry as I am using this as a test case for further calculations of Al-Cu solid solutions. 

Is there anything terribly wrong with my input? Should I impose symmetry despite the addition of Al to the Cu lattice? 

Thanks for your help.

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 &CONTROL
                 calculation = 'vc-relax' ,
                restart_mode = ?from_scratch? ,
                  wf_collect = .false. ,
                      outdir = './' ,
                  pseudo_dir = './' ,
                      prefix = 'Cu' ,
                      forc_conv_thr = 2.0d-2,
                      etot_conv_thr = 1.0d-3,
                     tstress = .true. ,
                   verbosity = 'minimal' ,
                   disk_io = 'none' ,
                     tprnfor = .true. ,
 /
 &SYSTEM
                       ibrav = 8,
                   celldm(1) = 9.505756,      
                   celldm(2) = 1.735408,
                   celldm(3) = 4.921944,
                         nat = 96,
                        ntyp = 1,
                     ecutwfc = 22 ,
                     ecutrho = 220 ,
                       nosym = .true. ,
                 occupations = 'smearing' ,
                     degauss = 0.022 ,
                    smearing = 'methfessel-paxton' ,
 /
 &ELECTRONS
                    conv_thr = 1.0d-5 ,
                 mixing_beta = 0.7 ,
 /
 &IONS
                ion_dynamics = 'bfgs' ,
 /
 &CELL
                       press = 0.0 ,
              press_conv_thr = 5.0d0,
                 cell_dofree = 'xyz' ,
               cell_dynamics = 'bfgs' ,
 /
ATOMIC_SPECIES
   Cu   63.54600  Cu.pw91-n-van_ak.UPF 
ATOMIC_POSITIONS (crystal)
Cu       0.000000000  -0.000082163  -0.000018624
...
K_POINTS automatic 
6 4 2 1 1 1 1 

===================================================================
Christopher J. O'Brien
cjobrien at ncsu.edu
https://sites.google.com/a/ncsu.edu/cjobrien/
See what I'm citing at http://www.citeulike.org/cjo123

Ph.D. Candidate
Computational Materials Group
Department of Materials Science & Engineering
North Carolina State University
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