[Q-e-developers] confirm interpretation on c_bands and suggest references on QE

[Jun Liu]

Dear Developers,

I understand the subroutine c_bands() the following way, and need an
experienced developer to confirm its correctness. Please correct me
whenever necessary, as correct interpretation would be crucial for my next
step of work.

In subroutine c_bands_k(), several loops are given to solve for eigenvalues
& eigenvectors (ev/vec), this is to avoid that a single CG might not
successfully reach the residue minimum, so restart CG several times to
ensure its convergence. For iteration beyond the second one, rotate_wfc()
is first called to calculate ev/vec by direct methods with Lapack, its
results are sent over to initialize the CG process in subroutine
ccgdiagg(), which is seen by noticing that psi is used in h_psi and s_psi
to get new H and S, to refine the results . During the whole process, H and
S are calculated on the fly and the underlying potentials and deeq are kept
unchanged unless the lattice itself changes.

The other favor you might do to me to understand the code in shortest time
is to help recommend some references on which the -notation- and -formulae-
used by the code are closely based. I have the following references by my
hand and found them useful, and would be really appreciated if I could be
suggested more relevant references on which QE is based.

>> David Vanderbilt_PhysRevB.41.7892, "soft self-consistent
pseudopotentials in a generalized eigenvalue formalism"
>> G. Kresse and D. Joubert_PhysRevB.59.1758, "From ultrasoft
pseudopotentials to the projector augmented-wave method"
>> J Ihm, Alex Zunger and Marvin L Cohen_J. Phys. C: Solid State Phys. 12
4409, "Momentum-space formalism for the total energy of solids"
>> P. E. Blochl, Phys. Rev. B 50, 17953 1994, "Projector augmented-wave
method"
>> R.M. Martin, Electronic Structure: Basic Theory and Practical Methods,
Cambridge University Press

Thank you very much,

-- 
Sincerely,
Jun
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