[Pw_forum] surface relaxation and non-zero parallel forces.
Gisela Bocan
gbocan at gmail.com
Sat Jun 11 20:54:20 CEST 2011
Hello,
Thanks for the reply. I did not make myself clear enough in the
previous post. Sorry for that. My final goal is to relax the surface but I
posted the file.in for a test 'scf' calculation to show the initial forces I
get. The relaxation obtained with the forces posted will not be just normal
to the surface. Even if I forced it to be, atoms within the same layer will
not relax equally. Making some further tests I managed to improve the
results by messing with mixing_beta (=0.1) and mixing_mode (='local-TF') but
the problem persists none the less for some values of the parameters (as the
one posted). I did reduce the density of k-points in later tests. In any
case, I think I finally succeded in solving the problem, at least for the
set of parameters I am interested in.
Again thanks for the quick reply!
Dr. G. A. Bocan.
Surface Physics Group,
Centro Atómico Bariloche.
On Sat, Jun 11, 2011 at 1:48 AM, mohnish pandey <mohnish.iitk at gmail.com>wrote:
> Dear Dr. Bocan,
> AS your input file suggest, you are not relaxing
> the system, you are doing the calculation for only one electronic cycle. As
> you have cleaved the bulk the atoms will relax upon cleaving and they wont
> be in the bulk-like position, so you must relax all of them. Put the flag
> "calculation" = "relax", it will minimize the forces and finally you will
> get the systems with atoms having force below the threshold value(you can
> use the default value in the code). And I think there is not need to use
> such a dense grid of k- points, I think 12x10x1 will suffice.
>
> On Sat, Jun 11, 2011 at 8:05 AM, Gisela Bocan <gbocan at gmail.com> wrote:
>
>> Hello,
>> I assumed surface relaxation for the Ag(110) surface would be an
>> easy matter. As it happens, I find non-zero forces parallel to the surface
>> and therefore, upon relaxation, I get a non-neglectable parallel
>> displacement of the ions. I am working with a 2x2sqrt(2) unit cell. I attach
>> my file.in and the forces I get. Note that the forces along one direction
>> (x) are much larger that along the other one (y). Note as well the large
>> values considered for ecutwfc, ecutrho, kpoints and the small degauss and
>> conv_thr. Any ideas on how to correct this behaviour? Am I missing
>> something? Thanks in advance and sorry if this is a stupid question. Small
>> changes in the input parameters can lower the forces I get but I find
>> nothing systematic.
>>
>> &control
>> prefix = 't_G0',
>> outdir = ' ',
>> pseudo_dir = '/home/qe/pseudo',
>> calculation = 'scf',
>> tprnfor = .true.,
>> lkpoint_dir = .false.,
>> verbosity = 'high',
>> /
>> &system
>> ibrav = 8,
>> celldm(1) = 11.1298607358762567,
>> celldm(2) = 1.4142135623730949,
>> celldm(3) = 2.25,
>> nat = 16,
>> ntyp = 1,
>> ecutwfc = 45,
>> ecutrho = 450.00,
>> occupations = 'smearing',
>> smearing = 'mv',
>> degauss = 0.002,
>> /
>> &electrons
>> conv_thr = 1.d-12
>> diagonalization = 'cg'
>> /
>> &ions
>> /
>> ATOMIC_SPECIES
>> Ag 107.8682 Ag.pbe-d-rrkjus.UPF
>> ATOMIC_POSITIONS crystal
>> Ag 0.0000000000000000 0.0000000000000000 0.3333333333333333
>> Ag 0.5000000000000000 0.0000000000000000 0.3333333333333333
>> Ag 0.0000000000000000 0.5000000000000000 0.3333333333333333
>> Ag 0.5000000000000000 0.5000000000000000 0.3333333333333333
>> Ag 0.2500000000000000 0.2500000000000000 0.2222222222222222
>> Ag 0.7500000000000000 0.2500000000000000 0.2222222222222222
>> Ag 0.2500000000000000 0.7500000000000000 0.2222222222222222
>> Ag 0.7500000000000000 0.7500000000000000 0.2222222222222222
>> Ag 0.0000000000000000 0.0000000000000000 0.1111111111111111
>> Ag 0.5000000000000000 0.0000000000000000 0.1111111111111111
>> Ag 0.0000000000000000 0.5000000000000000 0.1111111111111111
>> Ag 0.5000000000000000 0.5000000000000000 0.1111111111111111
>> Ag 0.2500000000000000 0.2500000000000000 0.0000000000000000
>> Ag 0.7500000000000000 0.2500000000000000 0.0000000000000000
>> Ag 0.2500000000000000 0.7500000000000000 0.0000000000000000
>> Ag 0.7500000000000000 0.7500000000000000 0.0000000000000000
>> K_POINTS automatic
>> 33 23 1 0 0 0
>>
>> atom 1 type 1 force = 0.00000000 0.00000000 -0.01175276
>> atom 2 type 1 force = 0.00000000 0.00000000 -0.01175282
>> atom 3 type 1 force = 0.00000000 0.00000000 -0.01175318
>> atom 4 type 1 force = 0.00000000 0.00000000 -0.01175325
>> atom 5 type 1 force = -0.00004221 0.00000033 0.01048323
>> atom 6 type 1 force = 0.00004221 0.00000033 0.01048323
>> atom 7 type 1 force = -0.00004221 -0.00000033 0.01048323
>> atom 8 type 1 force = 0.00004221 -0.00000033 0.01048323
>> atom 9 type 1 force = 0.00000000 0.00000000 -0.01048309
>> atom 10 type 1 force = 0.00000000 0.00000000 -0.01048306
>> atom 11 type 1 force = 0.00000000 0.00000000 -0.01048272
>> atom 12 type 1 force = 0.00000000 0.00000000 -0.01048269
>> atom 13 type 1 force = -0.00004148 0.00000003 0.01175266
>> atom 14 type 1 force = 0.00004148 0.00000003 0.01175266
>> atom 15 type 1 force = -0.00004148 -0.00000003 0.01175266
>> atom 16 type 1 force = 0.00004148 -0.00000003 0.01175266
>>
>> Dr. G. A. Bocan
>> Surface Physics Group,
>> Centro Atómico Bariloche,
>>
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>>
>
>
> --
> Regards,
> MOHNISH,
> -----------------------------------------------------------------
> Mohnish Pandey
> Senior Project Associate,
> Department of Chemical Engineering,
> IIT KANPUR, UP, INDIA
> -----------------------------------------------------------------
>
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