I want to optimize it using Gaussian 09, however its giving error #2070. What parameters should we chose for optimizing using DFT? The image of crystal structure is attached below.
Any clarifications will be appreciated.
Thanks
Greetings,
Your compound is not a discrete molecule, as you must know and as seen in the 3x3x3 packing attached. So, this implies that you should model it using periodic boundary conditions (PBC). For PBC, you can find the syntax and an example here https://gaussian.com/pbc/, the parameters that you can tweak are also shown in the same page.
Thankyou for the answer.
Isnt PBC already applied on the structure?
Are there any perticular parameters to select in PBC? I am sorry to ask these basics as i am new user
To make it easier, I'll try to use a generic example to create a gaussian input file for PBC. You'll have to input the keywords line with the theory level, and some parameters for checkpoint file, memory, processors, etc. Something like, for example:
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%chk=example_name.chk #name for checkpoint file
%nprocshared=256 # number of processors to employ
%mem=500GB # memory employed
# PBEPBE/6-31g(d,p)/Auto SCF=Tight opt #keywords line
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After that, you can leave a blank line, followed by a comment line, another blank line and then the charge and spin multiplicity for the unit cell:
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blank line
Comment for the calculation, title or something else
blank line
0 1 #charge and spin multiplicity
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After the charge/multiplicity you'll put the coordinates of your unit cell (for example, in cartesian):
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Ga 0.000000 0.000000 0.000000
Ga 0.000000 2.825000 2.825000
Ga 2.825000 0.000000 2.825000
Ga 2.825000 2.825000 0.000000
As 1.412500 1.412500 1.412500
As 1.412500 4.237500 4.237500
As 4.237500 1.412500 4.237500
As 4.237500 4.237500 1.412500
---------------------------------------------------------------------------------------------------------------
After the coordinates, you have to put a translation vector (TV) that tells gaussian the distance to repeat your unit cell following that vector, for a 3D case you'll need 3 TV for 3 directions:
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TV 5.650000 0.000000 0.000000
TV 0.000000 5.650000 0.000000
TV 0.000000 0.000000 5.650000
---------------------------------------------------------------------------------------------------------------
Leave a final blank line and the input is done, the full input file would be:
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%chk=example_name.chk
%nprocshared=256
%mem=500GB
# PBEPBE/6-31g(d,p)/Auto SCF=Tight opt
blank line
Comment for the calculation, title or something else
blank line
0 1
Ga 0.000000 0.000000 0.000000
Ga 0.000000 2.825000 2.825000
Ga 2.825000 0.000000 2.825000
Ga 2.825000 2.825000 0.000000
As 1.412500 1.412500 1.412500
As 1.412500 4.237500 4.237500
As 4.237500 1.412500 4.237500
As 4.237500 4.237500 1.412500
TV 5.650000 0.000000 0.000000
TV 0.000000 5.650000 0.000000
TV 0.000000 0.000000 5.650000
blank line
---------------------------------------------------------------------------------------------------------------
This calculation will create the system shown in the picture attached to this answer.
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