[Pw_forum] electric field in a hexagonal cell

[Kolb, Brian]

Hello,

I am trying to do a finite electric field calculation (lelfield = .true.) in
PWscf 4.1.1.  My system is hexagonal ice Ih.  Does anyone know if there are
any issues with running electric field calculations in hexagonal systems?
My numbers don't seem to be coming out right and I have noticed some
oddities in my output files.  I have run some tests on a single water
molecule in a large (30 bohr) hexagonal box.  I have noticed 2 things I
don't quite understand about the output.  First, when the code prints the
electric field I'm using in Cartesian coordinates, everything is fine.  But
the crystallographic coordinates it lists for the field don't seem to make
sense.  Here is the output there:

 Using Berry phase electric field
     In a.u.  cartesian system of reference
        0.0010000000
        0.0020000000
        0.0015000000
     In a.u.  crystal system of reference
        0.0011547005
        0.0014226497
        0.0015000000

Also, I'm not sure I understand the output of the dipole moment per unit
cell.  PWscf gives the electric and ionic dipole in cartesian coordinates.
But it prints some stuff above that that appear to be the same components of
the dipole.  The second two values there match the y and z components of the
dipole moment but the first value is nowhere near the x component given.
Here is the output for what I am talking about.

     Expectation value of exp(iGx):
(0.964011848451477,-5.995507655161780E-002)
  0.866025403784454
     Electronic Dipole per cell (a.u.) -0.726443072647282
     Ionic Dipole per cell (a.u.)   3.10083723173698

     Expectation value of exp(iGx): (0.853082198772715,0.385355036858273)
  0.866025403784500
     Electronic Dipole per cell (a.u.)   4.96219415632151
     Ionic Dipole per cell (a.u.)  -4.12250990107402

     Expectation value of exp(iGx):
(0.951667425345567,-9.247141385108108E-002)
   1.00000000000000
     Electronic Dipole per cell (a.u.)  -1.30811951649933
     Ionic Dipole per cell (a.u.)   1.10462319878209
Electronic Dipole on Cartesian axes
           1  -3.70374833901089
           2   4.96219415632151
           3  -1.30811951649933
Ionic Dipole on Cartesian axes
           1   3.10083723173698
           2  -4.12250990107402
           3   1.10462319878209

Basically, I was just wondering if anyone was aware of problems with PWscf
in using lelfield=.true. in hexagonal systems.  I don't have any trouble in
cubic systems, this only appears when I do hexagonal cells.

Thanks for your help.

Brian Kolb
Department of Physics
Wake Forest University
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