problem with forcing c2h symmetry

Hi all,
I am having problems forcing symmetry on this small transition metal cluster. It looks like NWchem is not able to recognize symmetry (c2h) even if I change the tolerances, and if I force the symmetry I obtain a geometry far away from what obtained with different codes (e.g. turbomole).
I am interested on the excited states of this dimer, therefore symmetry could be very handy, but if I try to do excitations with random phase approx on the optimized geometry I get instability problems, while activating the cis flag for the Tamm-Dancoff approx. generates negative excitations.
I do not know if I am doing something wrong in the input, and I will appreciate any suggestion.


START tio2_opt_c2hb3
GEOMETRY
symmetry group c2h
Ti -0.7073194 1.1604688 0.0000000
Ti 0.7073194 -1.1604688 0.0000000
O 0.0415349 -2.6445686 0.0000000
O 0.0000000 0.0000000 -1.2512390
O 0.0000000 0.0000000 1.2512390
O -0.0415349 2.6445686 0.0000000
END
BASIS

Ti library def2-TZVP

O  library def2-TZVP

END
DFT
xc B3LYP
direct
iterations 200
END
TASK DFT optimize



Thank you in advance,
Enrico

Hi Enrico,

There is indeed an issue with finding the symmetry for this system due to the way NWChem tries to find the symmetry.

In the mean time, the following geometry block will do what you want it to do:

GEOMETRY
symmetry group c2h
Ti 0.0000000 1.3590396 0.0000000
Ti 0.0000000 -1.3590396 0.0000000
O 1.3409217 -2.2797801 0.0000000
O -1.3409217 2.2797801 0.0000000
O 0.0000000 0.0000000 -1.2512390
O 0.0000000 0.0000000 1.2512390
END


Bert

Thank you Bert for your fast reply.
I have been working on your modified geometry but I end up again in a c2h optimized structure that is highly deformed and gives negative excitations (possible conical intersection?).

autosym is not able to detect the c2h symmetry on your modified geometry, therefore if I optimize it with c1 symmetry I get this minimum (which is very similar to the one I obtain with different codes with and without symmetry):

Ti 0.00000312 1.29508791 -0.41023362
Ti -0.00000292 -1.29508723 0.41023465
O 0.00002610 -2.57710993 -0.59171972
O -0.00002665 2.57710896 0.59172361
O -1.25308248 0.00005145 0.00001102
O 1.25308283 -0.00005117 -0.00001593


when I optimize your modified geometry with c2h symmetry I get this distorted structure:

Ti -0.26744804 1.30749556 0.00000000
Ti 0.26744804 -1.30749556 0.00000000
O 1.44788061 -2.71073052 0.00000000
O -1.44788061 2.71073052 0.00000000
O 0.00000000 0.00000000 -1.26048208
O 0.00000000 0.00000000 1.26048208


I tried to reoptimize the c2h one with no symmetry and I end up in a structure very close to the first one with no symmetry.
I cannot understand what could be the source of this problem.


Thanks,
Enrico