[Pw_forum] Lattice Constant Optimization of Aluminum

[PRASENJIT GHOSH]

Dear Paul,

You are getting zero forces because u have set
tprnfor= .false.
As a result the code is not at all calculating forces on the atoms.
For relaxation cal. u should have set it to .true.

Moreover ur unit cell has only one atom. Hence I don't think there is any
point in using the 'relax' option. Rather u can do a simple scf run and
still get the forces. With 'relax' option u can only relax the coordinates
of the atoms, not the unit cell.

With regards,
Prasenjit.

On Thu, April 26, 2007 9:11, Paul M. Grant said:
> To All:
>
> (BTW: PG: My last note on the "default" value of npk should have been
> termed
> "default maximum."  Sorry, but we Americans haven't spoken English since
> 1776.  Anyway, thanks for pointing me to the right Fortran routine.)
>
> I'm trying to do a very simple homework problem with PWscf.the
> optimization
> of the lattice constant of aluminum.
>
> Even with a wildly wrong first estimate of celldm(1) of 7.2 (the
> experimental value at RT is 7.665 au), I get zero net individual atomic
> forces and thus no optimization.  I've gotten "relax" in PWscf to work
> with
> a lot more complex polymer monoclinic unit cell containing eight atoms and
> two different elements.  So, I must be doing something really dumb
> (stupid).maybe I should be using vc-relax instead?  Anyway, here's the I/O
> (scusi e grazie):
>
> INPUT
>
> &control
>
>     title               = '$prefix_root$s$i.rx.in'
>
>     calculation                 = 'relax'
>
>     restart_mode = 'from_scratch',
>
>     prefix                        = '$prefix_root$s$i',
>
>     pseudo_dir                = '/home/pmpgrant/espresso-3.2/pseudo/',
>
>     outdir                        = '$home_root',
>
>     verbosity                   = 'minimal',
>
>     tprnfor                       = .false.,
>
>     tstress                      = .true.,
>
>  /
>
>  &system
>
>     ibrav              = 2,
>
>     celldm(1)                   = 7.2,
>
>     nat                            = 1,
>
>     ntyp              = 1,
>
>     ecutwfc                     = 15,
>
>     occupations               = 'smearing',
>
>     smearing                   = 'methfessel-paxton',
>
>     degauss                    = 0.05,
>
>     la2F              = .false.,
>
>  /
>
>  &electrons
>
>     diagonalization           = 'david',
>
>     conv_thr                    = 1.0d-12,
>
>     mixing_beta   = 0.7,
>
>  /
>
> &ions
>
>     ion_dynamics            = 'bfgs',
>
>     pot_extrapolation       = 'second-order',
>
>     wfc_extrapolation       = 'second-order',
>
> /
>
> ATOMIC_SPECIES
>
>  Al  26.98 Al.vbc.UPF
>
> ATOMIC_POSITIONS
>
>  Al 0.00 0.00 0.00
>
> K_POINTS {automatic}
>
> 32 32 32 0 0 0
>
> OUTPUT
>
> The total energy is the sum of the following terms:
>
>
>
>      one-electron contribution =     3.23304593 Ry
>
>      hartree contribution      =     0.01297127 Ry
>
>      xc contribution           =    -1.69806267 Ry
>
>      ewald contribution        =    -5.73107767 Ry
>
>      smearing contrib. (-TS)   =     0.00011533 Ry
>
>
>
>      convergence has been achieved
>
>
>
>      Forces acting on atoms (Ry/au):
>
>
>
>      atom   1 type  1   force =     0.00000000    0.00000000    0.00000000
>
>
>
>      Total force =     0.000000     Total SCF correction =     0.000000
>
>      SCF correction compared to forces is too large, reduce conv_thr
>
>
>
>
>
>      entering subroutine stress ...
>
>
>
>           total   stress  (Ry/bohr**3)                   (kbar)     P=
> 110.51
>
>    0.00075124   0.00000000   0.00000000        110.51      0.00      0.00
>
>    0.00000000   0.00075124   0.00000000          0.00    110.51      0.00
>
>    0.00000000   0.00000000   0.00075124          0.00      0.00    110.51
>
>
>
>
>
>      BFGS Geometry Optimization
>
>
>
>      bfgs converged in   1 scf cycles and   0 bfgs steps
>
>
>
>      End of BFGS Geometry Optimization
>
>
>
>      Final energy =      -4.1830078084 Ry
>
>
>
> CELL_PARAMETERS (alat)
>
>   -0.500000000   0.000000000   0.500000000
>
>    0.000000000   0.500000000   0.500000000
>
>   -0.500000000   0.500000000   0.000000000
>
>
>
> ATOMIC_POSITIONS (alat)
>
> Al       0.000000000   0.000000000   0.000000000
>
>
>
>
>
> Paul M. Grant, PhD
>
> Principal, W2AGZ Technologies
>
> Visiting Scholar, Applied Physics, Stanford University
>
> EPRI Science Fellow (Retired)
>
> IBM Research Staff Member Emeritus
>
>  <mailto:w2agz at pacbell.net> w2agz at pacbell.net
>
>  <http://www.w2agz.com/> http://www.w2agz.com
>
>
>
>
>
>
>
>


PRASENJIT GHOSH,
Ph. D STUDENT,
THEORETICAL SCIENCES UNIT,
JAWAHARLAL NEHRU CENTRE,
JAKKUR P. O.,
BANGALORE - 560064,
INDIA.

PHONE:+91-80-22082835 (OFFICE)
            +91 9880519401 (MOBILE)