What is the best method (in HF/DFT/CDFT) to calculate the off-diagonal coupling elements H_12 for electron/hole transfer in a molecule (intra-molecular electron/hole transfer) ? I have used CDFT-CI method in Qchem, but I am not getting accurate/good results. Is there any alternative method ?
Dear Nishat,
To simulate the electron-hole dynamics you have to use non-adiabatic molecular dynamics (NAMD). You can obtain the trajectory via any molecular dynamics simulation (this highly depends on your system) which in most cases is ab initio MD using DFT. After you obtained the trajectory you have to calculate the eigenvalues (energy levels) and eigenvectors (molecular orbitals) of each configuration at each time step. Then you can obtain the non-adiabatic couplings (NACs) between states at each time step using the Tully method (it uses a finite difference scheme).
PYXAID package is a nice one you can compute the NACs and propagate the electron-hole dynamics using fewest switches surface hopping (FSSH) algorithm. It interfaces with Quantum ESPRESSO. Please visit their website and read their papers for more information:
https://pubs.acs.org/doi/10.1021/ct400641n
https://akimovlab.github.io/
I also want to mention that depending on the system different calculations may affect the NACs significantly, for example the choice of basis set and functional, adding the spin-orbit coupling etc.
I hope it helps.
Dear Nishat,
According to your description, is it functional the key of the question? I mean, if you use TDDFT, then you can choose B3LYP, M06, PBE... they will give you quite different answers.
From my experience, HF will not be the best, because it lacks the electronic correlation. It hardly tells you a good answer. For small systems, I will use CASSCF or CI. For medium-sized or larger system, you have no choice but DFT and its variants, I think.
Cheers,
Yu
Yu Zhai Thanks for your answer.
1) Is there any other way without using TDDFT?
2) for small systems, to use CASSCF and CI, which software do you recommend? Also, can you provide me any sample example/source?
3) for larger systems, CDFT is good. But do you know any particular method to calculate the charge transfer integral?
Mohammad Shakiba Thanks for your answer. The methods you suggested, Can I do those in QCHEM or NWCHEM or Gaussian?
Nishat Tasnim Liza As far as I know it is possible to obtain the MOs in any quantum chemistry package in Kohn-Sham basis set. So, the only thing to do is to see how they are printed in those packages. Then you can use them to obtain the NACs but to propagate the electron-hole dynamics using NACs, you should use the PYXAID package since none of them contain the FSSH algorithm.
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