[Pw_forum] Bonding Energy

[Eyvaz Isaev]

Dear Michal,

I have just three comments:
1. You should not use only \Gamma point for small
systems (where number of atoms <10). Rather you have
to use integration via Monkhorst-Pack k-points which
are generated automatically if you enter:

K_POINTS{automatic}
10 10 10 
0 0 0 

which means that k-points will be generated according
to Monkhorst-Pack schem,  each direction of reciprocal
basis vectors is divided by 10 and there is no shift
of  origin of k-vectors.

2. celldim(i) are given in atomic units, so, if you
have lattice parameter of Pd which is 3.89Angstrom,
you can convert it to atomic unit using
1Ang=1./0.529177, i.e. 3.89Ang=3.89/0.529177 (a.u.)
For cubic structures only celldim(1) is required.

3. Probably, in the second script something is wrong.
You chose fcc lattice within 2 atoms. Sure, this
happens, but I suggest you should consider 2 atoms in
the simple cubic cell (like isolated atoms). If so,
you should vary (increase) cell parameter (celldim(1))
in order get isolated atoms.
 
Besides your 
> ATOMIC_POSITIONS{angstrom}
>  Ni 0.0 0.0 0.0
>  Ni $i  0.0 0.0
looks not correct. You mention {angstrom}, but I
suggest in your case it should be {alat}. Though it
depends on what do you want.  

What concerns good (really good) papers I advice
M.C.Payne, M.P.Teter et. al., Reviews of Modern
Physics, 64 (1992), p.1045.
It should be as just starting paper. 

Regards, 
Eyvaz. 
Theoretical Physics Department
Moscow Steel and Alloys Institute
 
--- Michal Lemieszewski <lemiesz at mitr.p.lodz.pl>
wrote:
> Dear PWscf users,
> 
> I have tried to calculate bonding energy between
> Ni-Ni and Pd-Pd. Then I
> would try to calculate energy of a layer.
> The file to calculate Ni-Ni I have used from
> example1 file and modify it to
> my case, but I got "strange" results (to both
> calculations).
> Therefore I have two questions involving my
> calculations:
> 1. Can PWscf make so type of calculations? If so can
> You tell my what am I
> doing wrong?
> 2. How can I calculate celldm(1) in general (for
> example for Pd), I know the
> cell parameters but I
> don't know how to translate them to celldm(1).
> I think it should be exact value (or could it be
> estimated?).
> 
> Please forgive me if those are trivial questions,
> but I am new in this field
> and I am learning ( I am undergraduate student).
> I also want to ask if You could recommend  me some
> articles or ("good") web
> pages about Ni, Pd (e.g. experimental values)
> k-points and
> things which You think I should read to understand
> more about program and my
> problem (catalysis).
> 
> I enclose example files for Ni.
> 
> Thanks,
>                 Michal
> 
> #
> # self-consistent calculation
> #
> cat > ni.scf0.in << EOF
>  &control
>     calculation='scf'
>     restart_mode='from_scratch',
>     pseudo_dir = '$PSEUDO_DIR/',
>     outdir='$TMP_DIR/'
>     prefix='ni'
>     tprnfor = .true.,
>     tstress = .true.
>  /
>  &system
>     ibrav=2, celldm(1) =6.48, nat=1, ntyp=1,
>     nspin = 2,  starting_magnetization(1)=0.7,
>     ecutwfc = 24.0, ecutrho = 288.0,
>     occupations='smearing',
> smearing='methfessel-paxton', degauss=0.02
>  /
>  &electrons
>     conv_thr = 1.0e-8
>     mixing_beta = 0.7
>  /
> ATOMIC_SPECIES
>  Ni 58.69 NiUS.RRKJ3.UPF
> ATOMIC_POSITIONS{angstrom}
>  Ni 0.0 0.0 0.0
> K_POINTS{gamma}
> EOF
> 
> #
> # self-consistent calculation
> #
> for i in `seq 1.0 0.1 5.0`;do
> cat > ni.scf$i.in << EOF
>  &control
>     calculation='scf'
>     restart_mode='from_scratch',
>     pseudo_dir = '$PSEUDO_DIR/',
>     outdir='$TMP_DIR/'
>     prefix='ni'
>     tprnfor = .true.,
>     tstress = .true.
>  /
>  &system
>     ibrav=2, celldm(1) =6.48, nat=2, ntyp=1,
>     nspin = 2,  starting_magnetization(1)=0.7,
>     ecutwfc = 24.0, ecutrho = 288.0,
>     occupations='smearing',
> smearing='methfessel-paxton', degauss=0.02
>  /
>  &electrons
>     conv_thr = 1.0e-8
>     mixing_beta = 0.7
>  /
> ATOMIC_SPECIES
>  Ni 58.69 NiUS.RRKJ3.UPF
> ATOMIC_POSITIONS{angstrom}
>  Ni 0.0 0.0 0.0
>  Ni $i  0.0 0.0
> K_POINTS{gamma}
> EOF
> 
> 
> 
> 
> 
> 
> 
> 
> 
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