[Pw_forum] A question about the wrong point group symmetries of one-dimensional structures

[Karim REZOUALI]

Hello everbody, 


I am trying to simulate some achiral (n ,0) [n= 5, 8, 10] zigzag carbon nanotubes in pw scf. 

The following input file is for (8,0): 

&control 
calculation = 'scf' 
restart_mode = 'from_scratch' 
title = 'cnt' 
verbosity = 'high' 
pseudo_dir = '', 
outdir= '' , 
prefix='cnt', 
tprnfor=.true., 
tstress=.true. 

/ 

&system 
ibrav= 0 
celldm(1) = 8.104120169, 
nat = 32, 
ntyp = 1, 
ecutwfc = 60.0, 
occupations = 'fixed', 

/ 
&electrons 
mixing_beta = 0.2 
conv_thr = 1.0d-9 
/ 
CELL_PARAMETERS (alat= 4.64872593) 
1 .00 0.00 0.00 
0.00 8 .00 0.00 
0.00 0.00 8.00 
ATOMIC_SPECIES 
C 12.0107 C.oncvpsp.upf 
ATOMIC_POSITIONS {angstrom} 
C 2.856428508022 3.209468929586 0.000000203 
C 3.576345516550 2.965158124213 -1.228208929314 
C 0.7121704998315 1.228210398531 2.965162731946 
C 1.432087508359 2.269433979920 2.269433692888 
C 2.856428508022 -2.269437387634 2.269437100602 
C 3.576345516550 -1.228208554289 2.965158279554 
C 0.7121704998315 -2.965162576605 -1.228210773556 
C 1.432087508359 -3.209464110352 0.000000203 
C 2.856428508022 0.000000203 -3.209468929586 
C 3.576345516550 -1.228208929314 -2.965158124213 
C 0.7121704998315 2.965162731946 -1.228210398531 
C 1.432087508359 2.269433692888 -2.269433979920 
C 2.856428508022 2.269437100602 2.269437387634 
C 3.576345516550 2.965158279554 1.228208554289 
C 0.7121704998315 -1.228210773556 2.965162576605 
C 1.432087508359 0.000000203 3.209464110352 
C 2.856428508022 -3.209468929586 -0.000000203 
C 3.576345516550 -2.965158124213 1.228208929314 
C 0.7121704998315 -1.228210398531 -2.965162731946 
C 1.432087508359 -2.269433979920 -2.269433692888 
C 2.856428508022 2.269437387634 -2.269437100602 
C 3.576345516550 1.228208554289 -2.965158279554 
C 0.7121704998315 2.965162576605 1.228210773556 
C 1.432087508359 3.209464110352 -0.000000203 
C 2.856428508022 -0.000000203 3.209468929586 
C 3.576345516550 1.228208929314 2.965158124213 
C 0.7121704998315 -2.965162731946 1.228210398531 
C 1.432087508359 -2.269433692888 2.269433979920 
C 2.856428508022 -2.269437100602 -2.269437387634 
C 3.576345516550 -2.965158279554 -1.228208554289 
C 0.7121704998315 1.228210773556 -2.965162576605 
C 1.432087508359 -0.000000203 -3.209464110352 
K_POINTS {automatic} 
8 1 1 0 0 0 

The point group symmetry of any achiral ( n , 0) CNT is al ways D2nh , but in the output of my calculations for the three nanotubes [n= 5, 8, 10] , the symmetry is D4h regardless of n value. 
I want to know i f there is a way to get the right symmetry ? 

Best, 

K 



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