I am trying to optimise anthracene in D2h point group, but every time after the optimisation is complete it shows as a C1 point group. How to fix that? I want the molecule to be optimised at D2h point group symmetry only.
write Z-matrix for it. You might need to use dummy atoms. Be aware that D2h minimum might be very close to the nonsymmetric minimum but also might be not a real minimum of PSE.
Thanks for your reply Dmitry Sharapa
I have now find the solution. I have used z-matrix format and given the following in the root line: # opt freq b3lyp/6-31+g(d,p) scf=xqc symmetry=(follow,pg=d2h)
The out put came with D2H symmetry.
Koushik Mondal Do we need to give dummy atoms to follow a particular point group?
It depends on the situation (molecule and point group). To build Z-matrix without dummy atoms quite often is possible but might be much more complex than with.
I have a 5-atom molecule with spin multiplicity and charge equal to 1 and -1, respectively. Although it's small, the geometry optimization at the CASSCF level using Gaussian 16 keeps giving me C1 instead of C3v (as the literature claims it to be). I am feeding the opt job with the active space previously converged (in line with the literature). Neither "opt + symmetry=(follow,pg=d2h)" nor "opt=z-matrix" can give C3v. Can anyone point me in the right direction?
C3v is not a subgroup of D2h, so there is no sense in pg=d2h, maybe pg=c3v
"opt=z-matrix" will have a sense if your z-matrix is built in the way to have C3v group (3 equal bond length, 3 equal angles, 2 dihedrals frozen to 120, if we are speaking of the molecule like Cl-CH3 / O=PCl3 )
X
Y R1 X
Z1 R2 Y A2 X
Z2 R2 Y A2 X 120 Z1
Z3 R2 Y A2 X 120 Z2
Variables
R1=
R2=
A2=
Hi, Dmitry. Thanks! There is a typo above. Sorry. I meant "opt + symmetry=(follow,pg=C3v)". I will try what you suggested. However, isn't freezing some coordinates equivalent to a "popt", which may not yield a global minimum at all?
yes, if your system is for example jan-teller, minimum HAS TO be out of maximal point group. And generally - a symmetrical structure is not obligatory a global minimum. It is not obvious to me why do you need CASSCF, maybe it is better first to optimize it as C3v on DFT and then start from optimized geometry in CAS.
Thank you! I will keep trying. I got the starting geometry from one of the papers on the topic. I just need the Hessian matrix, but they don't provide more than the Cartesian coordinates in the supporting information.
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