Controlling the occupations of molecular orbitals (occup)

[Tanvir ur Rahman Chowdhury]

Hello,

There is an example of controlling the occupations of molecular orbitals on the NWChem site without any further explanations.

occup

6 6 # core-hole in beta

1.0 0.0

1.0 1.0

1.0 1.0

1.0 1.0

1.0 1.0

0.0 0.0

end  

I understand this example might be enough for many users.

But for a new user like me, I am not quite sure what these numbers are. I would really appreciate any assistance to understand this.

Thanks in advance.

[Niri Govind]

Hi Tanvir,

>> I am not quite sure what these numbers are. 

The 6 6 corresponds to 6 alpha orbitals and 6 beta orbitals.

The remaining numbers are the occupations of the molecular orbitals starting from the lowest energy MO.

In this H2O example, we have a hole in the 1s beta orbital.

occup

6 6 # core-hole in beta

1.0 0.0

1.0 1.0

1.0 1.0

1.0 1.0

1.0 1.0

0.0 0.0

end  

On the other hand, the following example corresponds to the ground state occupation of the alpha and beta electrons

occup

6 6 # 

1.0 1.0

1.0 1.0

1.0 1.0

1.0 1.0

1.0 1.0

0.0 0.0

end  

Hope this helps. Let us know if you need further clarification.

Best,

-Niri 

Niri Govind

PNNL

niri....@pnnl.gov

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[Tanvir ur Rahman Chowdhury]

Hi Niri,

Thanks for your assistance. Let me know if I am wrong; to do a triplet calculation of C2 dimer, I have to write:

occup

7 5

1.0 1.0

1.0 1.0

1.0 1.0

1.0 1.0

1.0 1.0

1.0 0.0

1.0 0.0

end

And for a singlet C2 dimer:

occup

6 6

1.0 1.0

1.0 1.0

1.0 1.0

1.0 1.0

1.0 1.0

1.0 1.0

end

Thanks.

[niri....@gmail.com]

Hi Tanvir,

Yes. However, you don't need to use the occup block if you are trying to run C2 as a singlet or triplet.

Just set mult = 1 or mult =3 in your dft block and run it like a normal calculation.

Hope this helps.

Best,

-Niri

Niri Govind

PNNL

niri....@pnnl.gov