xas
Keywords
This option controls the details of simulating X-ray absorption spectroscopy with the target state optimization (TSO) DFT method.
elements
A list of heavy elements whose XAS is to be calculated.
| Value | Element list |
| Default | None |
For example, Qbics will calculate three XAS spectra for C, N, and O, respectively.
num_states
The number of excited states to be calculated for each core electron.
| Value | An integer |
| Default | 1 |
exclude
| Value | Atom range |
| Default | None |
The atoms whose XAS will not be calculated. For the input below:
xas
elements C
exclude 2-6
end
mol
C 1.20809735 0.69749533 0.
C 0.00000000 1.39499067 0.
C -1.20809735 0.69749533 0.
C -1.20809735 -0.69749533 0.
C -0.00000000 -1.39499067 0.
C 1.20809735 -0.69749533 0.
H 2.16038781 1.24730049 0.
H 0.00000000 2.49460097 0.
H -2.16038781 1.24730049 0.
H -2.16038781 -1.24730049 0.
H 0.00000000 -2.49460097 0.
H 2.16038781 -1.24730049 0.
end
Without exclude, Qbics will calculate core excitations for all 6 C atoms. However, since the 6 C atoms are equivalent, this is unnecessary. Thus, in exclude we assign atoms 2, 3, 4, 5, and 6, meaning that the calculation of core excitations for these 5 atoms is skipped.
Input Examples
Example: Calculate carbon and oxygen K-edge XAS for formaldehyde.
basis
# Since H does not have cc-pCVXZ basis set, we must assign basis sets individually.
# Unlike cc-pVXZ, cc-pCVXZ is optimized for core excitations, making it a better choice.
element
H cc-pVTZ
C cc-pCVTZ
O cc-pCVTZ
end
scf
charge 0
spin2p1 1
type U # It is better to use this.
end
xas
elements C O # For all heavy elements.
num_states 5
end
mol
C 0. 0.00000000 -0.53331338
O 0. 0.00000000 0.66490314
H 0. 0.93548358 -1.12356214
H 0. -0.93548358 -1.12356212
end
task
xas b3lyp
endExample:: Calculate carbon K-edge XAS for benzene, but only for one carbon since the remaining five are equivalent.
basis
# Since H does not have a cc-pCVXZ basis set, we have to assign them individually.
# Unlike cc-pVXZ, cc-pCVXZ is optimized for core excitations, so it is better to use.
element
H cc-pVTZ
C cc-pCVTZ
end
scf
charge 0
spin2p1 1
type U # It is better to use this.
end
xas
elements C # For all heavy elements.
num_states 3
exclude 2-6 # Only 1 carbon atom is calculated, since other 5 are equivalent to it.
end
mol
C 1.20809735 0.69749533 0.
C 0.00000000 1.39499067 0.
C -1.20809735 0.69749533 0.
C -1.20809735 -0.69749533 0.
C -0.00000000 -1.39499067 0.
C 1.20809735 -0.69749533 0.
H 2.16038781 1.24730049 0.
H 0.00000000 2.49460097 0.
H -2.16038781 1.24730049 0.
H -2.16038781 -1.24730049 0.
H 0.00000000 -2.49460097 0.
H 2.16038781 -1.24730049 0.
end
task
xas b3lyp
end