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<p>Dear Prof. Baroni.<br>
<br>
Thank you very much for your response.<br>
<br>
I'm very glad.<br>
<br>
>>by PWSCF, or are there plan to develop the excited state gradient calculation ? <br>
<br>
>>The implementation of TDDFT in PWSCf uses lanczos method and does not <br>
<br>
>>explicitly calculate the excited energy, and is it difficult to extend to <br>
<br>
>>calculate force in this formalism ? <br>
<br>
>the present implementation of tddft is particularly suited for the calculation of the entire spectrum of large systems, whereas excited-state energy gradients would require the calculation of individual eigenpairs <br>
>of the Liouvillian. That should not be difficult to implement, but it is not considered to be a priority at this time. Should anybody be interested in implementing this feature, we in Trieste would be delighted to help.<br>
<br>
Thank you for your advice.<br>
<br>
You mean if we diagonalize the Liouvillean operator by usual method instead of using Lanczos chain, and get <br>
<br>
eigenvalue and eigenvectors, we can get excited-state gradient ? <br>
<br>
Are there already formalism to calculate the excited energy gradient within occupied state only method ? <br>
<br>
Usual Casida's matrix, the dimension of the Matrix is \Omega_{i_j, k_q} where, i and j are occupied and unoccupied state (k and q are also occupied and unoccupied state pair), <br>
<br>
and the dimension is (2*Nc*Nv) * (2* Nc * Nv) where Nc and Nv is the number of the unoccupied and occupied states.<br>
<br>
But your Liouvillean matrix dimension is (2*Nv) * (2 *Nv), and it is very small than the usual Casida's one. <br>
<br>
It seems very attractive to perform the large molecule, because the possibilities to calculate the large molecule's excited state energy gradient is very important <br>
<br>
quantities in photochemistry. <br>
<br>
Sincerely, <br>
<br>
Yukihiro Okuno. <br>
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