Post Hartree-Fock HOMO-LUMO gap

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Hello NWChem community,

I am attempting to estimate HOMO-LUMO gaps (and UV absorption wavelength) with NWChem.

However, the module does not print HOMO-LUMO after the SCF cycle (for example, MP2, DFT, and CCSD(T) on H2 molecule).

How can I get NWChem to print out the HOMO-LUMO gap post-Hartree Fock energy for H2?

Also,is there a way for NWChem to print out whether HOMO-LUMO is sigma-sigma* or pi-pi* or anything like that?

Here is my input (last line modified for CCSD or SCF)


start molecule

title "Cytosine optimization"
charge 0

geometry units angstroms print xyz autosym
H 0.0 0.0 0.0
H 0.0 0.0 0.74

* library aug-cc-pVQZ

scratch_dir scratch


xc ssb-d

task dft energy

  • Huub Forum:Admin, Forum:Mod, NWChemDeveloper, bureaucrat, sysop
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Indeed the code does not print the HOMO-LUMO gap explicitly. However, at the end of the SCF or DFT calculation it will print the orbital analysis. For H2 (I have used SCF instead of DFT so I could simply use "task ccsd energy", and I used the cc-pvdz basis set) I got:

Vector    1  Occ=2.000000D+00  E=-5.924110D-01  Symmetry=a1g
MO Center= 0.0D+00, 0.0D+00, -4.0D-17, r^2= 7.1D-01
Bfn. Coefficient Atom+Function Bfn. Coefficient Atom+Function
----- ------------ --------------- ----- ------------ ---------------
1 0.403665 1 H s 6 0.403665 2 H s
2 0.173763 1 H s 7 0.173763 2 H s

Vector    2  Occ=0.000000D+00  E= 1.974400D-01  Symmetry=a2u
MO Center= 3.3D-17, 6.2D-17, -9.0D-16, r^2= 2.7D+00
Bfn. Coefficient Atom+Function Bfn. Coefficient Atom+Function
----- ------------ --------------- ----- ------------ ---------------
2 1.958656 1 H s 7 -1.958656 2 H s
1 0.150244 1 H s 6 -0.150244 2 H s

In this table "Occ" refers to the orbital occupation and "E" to the corresponding orbital energy. So it is relatively easy to identify vector 1 as the HOMO and vector 2 as the LUMO, giving a HOMO-LUMO gap of 0.19744 - -0.59241 = 0.78985 Hartree. Of course if you want you can write a little script to extract that information. I am more than happy to put that in our contrib directory, so you have it in future.

Best wishes, Huub

Just Got Here
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What should you do if you want gaps that are 0.1 hartree or less?

Just Got Here
Threads 2
Posts 4
What should you do if you want gaps that are 0.1 hartree or less?

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