Applying scissor operator in PYXAID program

[Yoonhoo Ha]

I have tried to carry out a NA-MD simulation for some system. But I have found a underestimated bandgap energy as a result of using PBE funtional, so I would like to apply the scissor operator to correct this.

I found a variable declared as shift_E in /PYXAID/scr_cpp/state.cpp file, but I don't have idea how to use it.

Best regards,

Yoonhoo Ha

[Wei Li]

Hi Yoonhoo,

not sure if you have got this question answered.

When you run step3, for params["states"].append(["S1",[2,-2,3,-4],0.00]), change the last value, 0.00, to any value you want to apply the scissor operator.

Wei

[Alexey Akimov]

Hi Yoonhoo,

As Wei Li suggest, the last parameter in the state definition is the energy correction. Lets say, you have a HOMO-LUMO gap from PDF to be 1.0 eV and it is underestimated with respect to say 2.0 eV what you know is right (e.g. experiment). Then you could define you ground and excited states as:

gs = ["GS", [2,-2, 3,-3], 0.0]

and

ex1 = ["S1", [2,-2,3,-4], 1.0]

Here, index 3 corresponds to the HOMO and 4 to the LUMO, so the gs -> ex1 is essentially HOMO->LUMO. In the definition of the ex1 state, you shift its energy by 1.0 eV, because you know that the DFT gap is underestimated.

Hope this helps.

Alexey