[DFTB-Plus-User] Reliability of prediction on conduction band of silicon nano crystals

[ZHAOHUI HUANG]

Hello,

    Sorry to bother you if not interested.

    Last fall semester, I sent a message to DFTB+ list and ask if it is possible to solve large size TB Hamiltonian. the feedback said the largest possible size of H is roughly 60,000 for LAPACK routine. Since my silicon mesoscale crystal can easily run up to a few hundreds of thousand of atoms, like 100,000 silicon atoms, I cannot use DFTB+, so I write a MPI TB code with sp3d5s* basis to calculate, based on implicitly restarting arnoldi method (IRAM) as well as intel distributed LU factorization for sparse matrix. I aim at only achieving bands near band gap. Now it works. Here I want to ask DFTB+ community again,

   What is the algorithm to relax the structure? see if I can embed my code into DFTB source, if DFTB relaxation is based on Lanczos method or its derivatives or whatever based on invariant space approach.

   For the above basis, how reliable are prediction of conduction bands, except the lowest one? If I use TB conduction bands, a few thousands, is it possible to calculation response function for my mesoscale crystal? like epsilon, based on TB conduction bands. comments are welcome! thanks a lot 


ZhaoHui Huang,