[Q-e-developers] lsym in projwfc.x

[Guido Fratesi]

Dear QE-developers,

the flag "lsym" in projwfc.x turns ON/OFF (default: ON) the 
symmetrization of the atomic states.

If .false., the partialdos is not computed. While this check is 
generally necessary to compute the DOS integrated on the full BZ by 
performing the summation only over the irreducible one, it is too 
restrictive when computing the DOS in special cases.

In particular, if you want to compute the bands of a system that has 
some symmetry (e.g. px=py for a square lattice) that is not retained by 
the k-point path for example from k=(0,0,0) to k=(1/2,0,0). In that 
case, lsym=.true. would produce the same result for px and py also at 
k/=(0,0,0). To disentangle them, it is sufficient to remove the 
check(*). This applies to the case "kresolveddos=.true".

Practically, my tiny suggestion is to replace the check "IF (lsym) THEN" 
in PP/src/projwfc.f90 with "IF (lsym .OR. kresolveddos) THEN"



      ELSE IF ( lsym .OR. kresolveddos ) THEN
         IF (noncolin) THEN
            CALL partialdos_nc (Emin, Emax, DeltaE, kresolveddos, filpdos)
         ELSE
            CALL partialdos (Emin, Emax, DeltaE, kresolveddos, filpdos)
         ENDIF
      ENDIF


and to change the specification of the variable in the input file 
PP/Doc/INPUT_PROJWFC.def  as:

if .true. the projections are symmetrized and partial density of states computed.
if .false. the projections are symmetrized; partial density of state are computed only in the k-resolved case.


On the contrary, I still don't see a case where one would set 
lsym=.false., kresolveddos=.false., and still like to compute the 
partial DOS.

Kind regards,

Guido


(*) alternatively, one could remove the symmetry by straining the 
lattice. I tested it by taking a square lattice, lsym=.false., and the 
same strained by 0.01% and the results are indeed equivalent.

-- 
Guido Fratesi

Dipartimento di Fisica
Universita` degli Studi di Milano
Via Celoria 16, 20133 Milano, Italy

Phone: +39 02 503 17348
email: guido.fratesi at unimi.it
web:   https://sites.google.com/site/guidofratesi/



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