[Q-e-developers] Questions about BFGS

[Paolo Giannozzi]

Dear Chen (Bonnie)

the proper place where to ask such questions is the pw_forum at pwscf.org.
Anyway:
- there are better pseudopotentials than the FHI ones, especially when
nasty elements like Ce are present
- I don't know about the specific material, but it is not likely that you
will get sensible results from simple PBE in a material containing Ce
- there is no point in having ecutrho > 4*ecutwfc with norm-conserving
pseudopotentials (FHI ones are)
- the threshold for self-consistency (conv_thr) is too large: it should be
set to 10^-6 or smaller
- the threshold for force convergence (force_conv_thr) is way too small:
try 10^-4 or larger
- same for threshold for energy convergence (force_conv_thr)

Paolo

On Wed, Jul 13, 2016 at 10:42 AM, Chen (Bonnie) Wang <chenbon at mit.edu>
wrote:

> Hi,
>
> I am an undergrad at MIT doing research regarding an orthorhombic BaCeO3
> crystal structure (please see below for the input file). I have been trying
> to find the ground state energy for the unit cell, but my output files have
> not given me the final energies, and these errors below show up.
>
> *Input: *
>
> &CONTROL
>  calculation = "relax"
>  restart_mode = "from_scratch"
>  verbosity = "low"
>  outdir = "./tmp/"
>  pseudo_dir = "./"
>  etot_conv_thr = 1.0D-5
>  forc_conv_thr = 1.0D-6
>  max_seconds = 172800.0
>  nstep = 500
> /
> &SYSTEM
>  ibrav = 0
>  ntyp = 3
>  nat = 20
>  tot_charge = 0.0
>  ecutwfc   = 165.D0
>  ecutrho = 1320.D0
> /
> &ELECTRONS
>  electron_maxstep = 500
>  conv_thr    = 1.D-5
> /
> &IONS
>  ion_dynamics = "bfgs"
> /
> &CELL
>  cell_dynamics = "none"
> /
> CELL_PARAMETERS angstrom
> 6.2153 0.0 0.0
> 0.0 8.7763 0.0
> 0.0 0.0 6.2347
> ATOMIC_SPECIES
> Ce 140.116 Ce.pbe-mt_fhi.UPF
> Ba 137.327 Ba.pbe-mt_fhi.UPF
> O  15.999 O.pbe-mt_fhi.UPF
> ATOMIC_POSITIONS crystal
> O 0.1984 0.0506 0.3043
> O 0.6984 0.4494 0.1957
> O 0.8016 0.5506 0.6957
> O 0.3016 0.9494 0.8043
> O 0.8016 0.9494 0.6957
> O 0.3016 0.5506 0.8043
> O 0.1984 0.4494 0.3043
> O 0.6984 0.0506 0.1957
> Ba 0.43716 0.25 0.01556
> Ba 0.93716 0.25 0.48444
> Ba 0.56284 0.75 0.98444
> Ba 0.06284 0.75 0.51556
> O 0.5328 0.25 0.6005
> O 0.0328 0.25 0.8995
> O 0.4672 0.75 0.3995
> O 0.9672 0.75 0.1005
> Ce 0.0 0.0 0.0
> Ce 0.5 0.5 0.5
> Ce 0.0 0.5 0.0
> Ce 0.5 0.0 0.5
> K_POINTS gamma
>
> *Error Messages: *
>
> 1. The energy_new is clearly shown as the same as the energy_old, but it
> is not what is displayed under "CASE."
>
> [image: Inline image 1]
>
> 2. At the end of the simulation this message shows up. What does the
> "maximum number of steps" referring to? I discussed with my supervisor, and
> he told me that the conv_thr should not be reduced, so I couldn't use that
> to solve my problem. And the final atomic coordinates are the same as my
> initial coordinates.
>
> [image: Inline image 2]
> [image: Inline image 4]
>
> If you have any suggestions on how to correct these errors, that would be
> great! Thank you so much!
>
> Best,
> *Chen (Bonnie) Wang*
> Department of Materials Science and Engineering
> Massachusetts Institute of Technology | 2017
> chenbon at mit.edu | (505) 600-5828
>
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>
>


-- 
Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222
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