[Pw_forum] PWscf vs. CP

[Axel Kohlmeyer]

On Wed, 18 Apr 2007, Peter Winey wrote:

PW> Dear all,
PW> 
PW> I was doing an electronic minimization using the CPV code cp.x. To make sure
PW> I did
PW> not make mistakes, I also did a similar calculation using the PWscf code
PW> pw.x.
PW> 
PW> Well, when I compared the results, I found quite some difference,
PW> in particular,
PW> the forces acting on atoms are quite different while the total energy are
PW> close.

there can be a number of reasons for this, but first please
give us an example for what you consider a large difference 
in the forces.

cheers,
   axel.


PW> 
PW> My question is whether I should expect to get same results from the two
PW> codes?
PW> If so, there must be something wrong with the input files that I used (see
PW> below).
PW> 
PW> Thanks in advance for any suggestions that you may have!
PW> 
PW> -Peter
PW> 
PW> --------------------------pw.x input file---------
PW> C2H4
PW>  &control
PW>     calculation='scf'
PW>     restart_mode='from_scratch',
PW>     wf_collect=.true.,
PW>     prefix='pwscf',
PW>     pseudo_dir = '/espresso-3.0/pseudo',
PW>     outdir='.',
PW>     tprnfor=.true.
PW>  /
PW>  &system
PW>                        ibrav = 1
PW>                    celldm(1) = 37.7945197733
PW>     nat=6, ntyp=2,
PW>     ecutwfc = 30.0,
PW>     occupations='fixed',
PW>  /
PW>  &electrons
PW>     conv_thr =  1.0d-8
PW>     mixing_beta = 0.7
PW>  /
PW> ATOMIC_SPECIES
PW> C   12.0107 C.pbe-van_ak.UPF
PW> H   1.00794 H.pbe-van_ak.UPF
PW> K_POINTS {gamma}
PW> ATOMIC_POSITIONS {crystal}
PW> C 0.46664509 0.5 0.5
PW> C 0.53335491 0.5 0.5
PW> H 0.43793698 0.5 0.45351762
PW> H 0.56206302 0.5 0.45351762
PW> H 0.56206302 0.5 0.54648238
PW> H 0.43793698 0.5 0.54648238
PW> 
PW> --------------------------cp.x input file---------
PW>  &control
PW>     calculation='cp',
PW>     restart_mode='from_scratch',
PW>     ndr=52, ndw=53,
PW>     nstep=400, iprint=10, isave=50,
PW>     dt=5.0,
PW>     etot_conv_thr  = 1.d-9,
PW>     ekin_conv_thr  = 1.d-5,
PW>     prefix = 'cp'
PW>     pseudo_dir='/espresso-3.0/pseudo/',
PW>     tprnfor = .TRUE.
PW>     outdir='.',
PW>  /
PW>  &system
PW>                        ibrav = 1
PW>                    celldm(1) = 37.7945197733
PW>     nat=6, ntyp=2,
PW>     ecutwfc = 30.0,
PW>  /
PW>  &electrons
PW>     electron_dynamics='damp'
PW>  /
PW>  &ions
PW>     ion_dynamics='none',
PW>  /
PW> ATOMIC_SPECIES
PW> C   12.0107 C.pbe-van_ak.UPF
PW> H   1.00794 H.pbe-van_ak.UPF
PW> ATOMIC_POSITIONS {crystal}
PW> C 0.46664509 0.5 0.5
PW> C 0.53335491 0.5 0.5
PW> H 0.43793698 0.5 0.45351762
PW> H 0.56206302 0.5 0.45351762
PW> H 0.56206302 0.5 0.54648238
PW> H 0.43793698 0.5 0.54648238
PW> 

-- 
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Axel Kohlmeyer   akohlmey at cmm.chem.upenn.edu   http://www.cmm.upenn.edu
   Center for Molecular Modeling   --   University of Pennsylvania
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