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[verstraete@pcpm.ucl.ac.be]

Hello,

Excellent work! You looked at the FAQ! However you didn't send us your 
output (eventually edited to be manageable). Netiquette... Anyway:

You are simulating a linear string of 4 C atoms in vacuum. Your cell looks 
huge: having a cell that is large (VdW distances between fragments in the 
supercell) but not well insulated (>8 or 10 A or even more in bad cases) 
will give rise to instabilities. RF calculations are even more delicate 
and unstable. Note that your coordinates are in A but your cell is in 
bohr...

You probably don't need all those kpoints, but that shouldn't be the 
problem. The diemac value is ok and important when you have vacuum. Are 
you sure you only want perturbations wrt atoms 2 to 3 (rfatpol) along only 
z? - I presume so

For the convergence, if the system is almost "metallic" (which is probably 
the case given the symmetry) you can have convergence problems and 
divergencies. You can try increasing the number of bands, but again it 
would be easier to look at your output. Is it converging really slowly, or 
diverging? Are you sure the GS was correctly converged beforehand?

You could start the dtset 2 with iscf 5, and set nstep to stop it before 
it stalls due to 13 restarts, then read in the 1WF (ird1wf2 1) and re-do 
the dtset 2.

Matthieu

--
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Matthieu Verstraete             mailto:verstraete@pcpm.ucl.ac.be 
PCPM, Boltzmann, pl. Croix du Sud, 1        tel: +32 10 47 33 59
B-1348 Louvain-la-Neuve  Belgium            fax: +32 10 47 34 52