# opt TD(singlets,nstates=3) uB3LYP/6-31g(d,p)
# opt TD(singlets,nstates=3) B3LYP/6-31g(d,p)
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Im currently trying to elucidate the photochromic mechanism, so I want to find the excited state stable geometry by Gaussian calculations. In uB3LYP and B3LYP, I have obtained similar structures, but detailed bond lengths/angles can be quite different.
Should I stick to results of uB3LYP or default spin one?
remained 0 before and after annihilation.
When you have unpaired electron in your system it's better to use spin unrestricted DFT which is called spin-polarized DFT or Local Spin DFT(LSDFT).
In LSDFT, the net spin density is the difference between the density of up-spin and down-spin electrons and the total electron density is the sum of the electron densities of up-spin and down-spin electrons. Also, for solving Khon-Sham equations you have 2 sets of wave functions: one for up-spin electrons one for down-spin electrons. In the restricted one, you are using the same wave function for up-spin and down-spin electrons which gives you different answer from the unrestricted calculations.
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