ABINIT Discussion Forums

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.

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Erkan Tetik

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

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".

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

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?