For a spin-polarized calculation (where nspin=2 in the INPUT), let's say you want to excite a spin-up (spin component 1) or spin-down (spin component 2) electron from the ground state to the excited state.

To do this, you will need to do the following:

• Find out how many bands do you have. You can obtain that by search for NBANDS in the running_*.log file
• Find out how many k points do you have. Let's call that number N_K.
• Find out how many electrons are occupying spin components 1 and 2. Let's say there are O_UP electrons that occupy the spin up, O_DN electrons that occupy the spin down.
• Next, calculate how many states are empty in both spins: empty states in the spin up = U_UP where U_UP = NBANDS - O_UP. Same applies for U_DN.

Finally, add the ocp_set as follows:

• ocp_set [O_UP-1]*1.0 1*0.0 1*1.0 [U_UP-1]*0.0 <repeated N_K times> [O_DN]*1.0 [U_DN]*0.0 <repeated N_K times>

Note the <repeated N_K times> above. It means: repeat [O_UP-1]*1.0 1*0.0 1*1.0 [U_UP-1]*0.0 for N_K times.

Let's have an example. Let's say we have 8 kpoints in both spins, 216 bands, where the spin up electrons occupy 144 bands and the spin down occupy 142 bands. Then, here are the two tags:

• ocp_set 143*1.0 1*0.0 1*1.0 71*0.0 143*1.0 1*0.0 1*1.0 71*0.0 143*1.0 1*0.0 1*1.0 71*0.0 143*1.0 1*0.0 1*1.0 71*0.0 143*1.0 1*0.0 1*1.0 71*0.0 143*1.0 1*0.0 1*1.0 71*0.0 143*1.0 1*0.0 1*1.0 71*0.0 143*1.0 1*0.0 1*1.0 71*0.0 142*1.0 74*0.0 142*1.0 74*0.0 142*1.0 74*0.0 142*1.0 74*0.0 142*1.0 74*0.0 142*1.0 74*0.0 142*1.0 74*0.0 142*1.0 74*0.0

I hope that helps!

More information can be found at: https://abacus.deepmodeling.com/en/latest/advanced/input_files/input-main.html#ocp-set