[QE-users] vc-relax for getting polymer bond lengths gives error in overlap matrix

[MARIA CATERINA CEVALLOS BRENES]

El 06-08-2019 09:28, MARIA CATERINA CEVALLOS BRENES escribió:

> Dear QE community: 
> 
> I am having several errors when trying to get the relaxed structure of polyacetylene. I am supposed to get 1.36 and 1.43 as the dimer bond lengths (for C=C and C-C respectively). 
> 
> I am using vc-relax method, just allowing z lattice parameter (along the chain) to change. 
> 
> Here is my input file: 
> 
> &control 
> 
> calculation = 'vc-relax', 
> 
> prefix = 'pa', 
> 
> verbosity = 'low', 
> 
> pseudo_dir = '/home/ccevallos/pslibrary.1.0.0/pbe/PSEUDOPOTENTIALS', 
> 
> outdir = './tmp', 
> 
> wf_collect=.true. 
> 
> / 
> 
> &SYSTEM 
> 
> ibrav = 0, 
> 
> nat=4, 
> 
> ntyp=2, 
> 
> ecutwfc=200.00, 
> 
> occupations = 'fixed', 
> 
> input_DFT='PBE', 
> 
> nbnd= 12, 
> 
> / 
> 
> &ELECTRONS 
> 
> / 
> 
> &ions 
> 
> / 
> 
> &cell 
> 
> cell_dofree='z' 
> 
> / 
> 
> ATOMIC_SPECIES 
> 
> C 12.011 C.pbe-n-rrkjus_psl.1.0.0.UPF 
> 
> H 1.00784 H.pbe-rrkjus_psl.1.0.0.UPF 
> 
> CELL_PARAMETERS {angstrom} 
> 
> 5.000000000000000   0.000000000000000   0.000000000000000 
> 
> 0.000000000000000   5.000000000000000   0.000000000000000 
> 
> 0.000000000000000   0.000000000000000   2.4 
> 
> ATOMIC_POSITIONS {angstrom} 
> 
> C 2.8 0 0 
> 
> C 2.1 0 1.16 
> 
> H 3.89 0 0 
> 
> H 3.19 0 1.16 
> 
> K_POINTS automatic 
> 
> 2 2 25 1 1 1 
> 
> However I am getting the following error: 
> 
> Error in routine cdiaghg (30): 
> 
> S matrix not positive definite 
> 
> What am I doing wrong? I also tried using a larger supercell, with 4 Carbon atoms, and it gives the same error, but you can see the bond length getting closer to 1.39 for al C-C bond lengths. In the latter case, why am I not observing the Peierls distortion?  
> 
> Thank you very much in advance! 
> 
> Best regards, 
> 
> Caterina Cevallos. 
> 
> QCLab. University of Costa Rica
> 
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There are two errors with the input file: 

Last atomic position should be: 

H 1.01 0 1.16  

and nbnd=10  

However, I'm still not getting the dimerization expected. 

  

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------
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