space group of 2,2 Carbon Nanotube

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ErkanTetik
Posts: 6
Joined: Thu Jan 14, 2010 1:04 pm

space group of 2,2 Carbon Nanotube

Post by ErkanTetik » Tue Mar 02, 2010 1:11 pm

Hello,

I have studied with the (2,2) Carbon Nanotube optimizasyon. The angdeg parameter is 90 90 120. I'm waiting a hexagonal structure for space group. But, space group is the "Symmetries : space group P2/m (# 10); Bravais mP (primitive monocl.)". Is it consistent with this space group?. I can not find where I made a mistake.
My input file is attached.

Thanks in advance for your help.
ragards.

----------------------
Erkan Tetik
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mverstra
Posts: 655
Joined: Wed Aug 19, 2009 12:01 pm

Re: space group of 2,2 Carbon Nanotube

Post by mverstra » Tue Mar 02, 2010 1:29 pm

Hello,

1) your positions are not precise enough for abinit to recognize symmetry operations (they need to be precise to within http://www.abinit.org/documentation/hel ... tml#tolsym)

2) your nanotube will not have 6 fold symmetry, so the space group will certainly not be 6-XXX. The Bravais lattice is still hexagonal of course, but what counts is the space group.

Matthieu
Matthieu Verstraete
University of Liege, Belgium

ErkanTetik
Posts: 6
Joined: Thu Jan 14, 2010 1:04 pm

Re: space group of 2,2 Carbon Nanotube

Post by ErkanTetik » Tue Mar 02, 2010 5:09 pm

hello,

there are 8 atoms in the 2,2 carbon nanotube, so i used this atom positions. what can i do for the abinit to recognize symmetry operations? moreover, i don't change the tolsym parameter. Because, i get a error that this error is the "This name(tolsym) is not one of the registered input variable names".

mverstra
Posts: 655
Joined: Wed Aug 19, 2009 12:01 pm

Re: space group of 2,2 Carbon Nanotube

Post by mverstra » Sat Mar 06, 2010 6:08 pm

tolsym has been introduced only in the latest version of abinit (6.0).

What you should do is determine the positions more precisely than 4 digits: find the angle between the atoms and add more precision to your positions. Then abinit will recognize the additional symops (probably some 2 axes and mirrors). If you want the full 4-fold symmetry you should use an orthogonal cell whose Bravais lattice is compatible with your tube.

Matthieu
Matthieu Verstraete
University of Liege, Belgium

ErkanTetik
Posts: 6
Joined: Thu Jan 14, 2010 1:04 pm

Re: space group of 2,2 Carbon Nanotube

Post by ErkanTetik » Thu Apr 15, 2010 5:53 pm

I'm trying the various calculations(geometric optimization) for CNT(5,0) and cnt(8,0) for days but I could not obtain the space group for CNT. For example(for cnt(8,0));
i use the tubegen package program to obtain the atomic positions of CNT. firstly, i calculate for optimization of cnt;

optcell 1
ionmov 3
ntime 100
dilatmx 1.05
ecutsm 0.5

then, i calcualate again again for new acell and atomic positions variables, for acell and atomic positions values;
i change the tolsym variable(i use the abinit 6.0.1) and i calculate again these variables.

Afterwards,
i calculate for optcell = 0 to find only atomic positions optimization.
i change again the tolsym variable and i calculate again these variables.

I have not obtained that i want space group for CNT. I except as space group : 186, 190 or 194 but It is calculated as 35.
i use the XcrySden program to find the angle between the atoms that it is such as 120.54, 118.28, 119,56.
What should I do to find correct space group or where do I make a mistake?

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