Bulk Nickel (and possibly other newbie questions)

Marcella Iannuzzi marci... at gmail.com
Fri Aug 15 23:05:37 CEST 2014


Hi

Just few remarks.

For the fcc bulk Ni energy, you need to construct a supercell, since there 
is no k-point sampling,
and check the convergence of the result with system size.

PADE is probably not an optimal choice for the XC functional, anyway, you 
should use consistent potential and basis set,
i.e. for the same number of valence electrons (in your input, the PP is for 
10 v.e. and the BS for 18)

If you don't specify in in the input, no spin polarisation is considered.

Regards

Marcella
  

On Friday, August 15, 2014 10:19:59 PM UTC+2, Alex wrote:
>
> Hi all,
>
> I am very new to DFT calculations, let alone CP2k, so some level of idiocy 
> on my part should be expected.
> As a simple test, I am trying to calculate the binding energy of a Ni atom 
> in a bulk crystal. The relevant portion of the input shown below:
>
> ***
> &GLOBAL
>   PROJECT Ni_inp_test
>   RUN_TYPE ENERGY_FORCE
>   PRINT_LEVEL LOW
> &END GLOBAL
> &FORCE_EVAL
>   METHOD Quickstep
>   &SUBSYS
>     &KIND Ni
>       ELEMENT Ni
>       BASIS_SET DZV-GTH-PADE-q18
>       POTENTIAL GTH-PADE-q10
>     &END KIND
>     &CELL
>       A     1.765000    1.765000    0.000000
>       B     0.000000    1.765000    1.765000
>       C    1.765000    0.000000    1.765000
>       PERIODIC XYZ
>     &END CELL
>     &COORD
>       Ni    0.000000000    0.000000000    0.000000000
>     &END COORD
>   &END SUBSYS
>   &DFT
>     BASIS_SET_FILE_NAME  BASIS_SET
>     POTENTIAL_FILE_NAME  GTH_POTENTIALS
>     &QS
>       EPS_DEFAULT 1.0E-10
>     &END QS
>     &MGRID
>       NGRIDS 4
>       CUTOFF 300
>       REL_CUTOFF 60
>     &END MGRID
>     &XC
>       &XC_FUNCTIONAL PADE
>       &END XC_FUNCTIONAL
>     &END XC
>     &SCF
>       SCF_GUESS ATOMIC
>       EPS_SCF 1.0E-7
>       MAX_SCF 300
>       ADDED_MOS 10
>       &DIAGONALIZATION  ON
>         ALGORITHM STANDARD
>       &END DIAGONALIZATION
>       &MIXING  T
>         METHOD BROYDEN_MIXING
>         ALPHA 0.4
>         NBROYDEN 8
>       &END MIXING
>       &SMEAR ON
>         METHOD FERMI_DIRAC
>         ELECTRONIC_TEMPERATURE [K] 300
>       &END SMEAR
>     &END SCF
>   &END DFT
>   &PRINT
>     &FORCES ON
>     &END FORCES
>   &END PRINT
> &END FORCE_EVAL
>
> ***
>
> This yields a total energy of E1=-35.155 a.u. after convergence.
>
> Then I decided to calculate the "vacuum" energy of an isolated atom, input 
> below:
>
> &GLOBAL
>   PROJECT Ni_inp_test
>   RUN_TYPE ENERGY_FORCE
>   PRINT_LEVEL LOW
> &END GLOBAL
> &FORCE_EVAL
>   METHOD Quickstep
>   &SUBSYS
>     &KIND Ni
>       ELEMENT Ni
>       BASIS_SET DZV-GTH-PADE-q18
>       POTENTIAL GTH-PADE-q10
>     &END KIND
>     &CELL
>       A     30.00000    0.000000    0.000000
>       B     0.000000    30.00000    0.000000
>       C    0.000000    0.000000    30.00000
>     &END CELL
>     &COORD
>       Ni    0.000000000    0.000000000    0.000000000
>     &END COORD
>   &END SUBSYS
>   &DFT
>     BASIS_SET_FILE_NAME  BASIS_SET
>     POTENTIAL_FILE_NAME  GTH_POTENTIALS
>     &QS
>       EPS_DEFAULT 1.0E-10
>     &END QS
>     &MGRID
>       NGRIDS 4
>       CUTOFF 300
>       REL_CUTOFF 60
>     &END MGRID
>     &XC
>       &XC_FUNCTIONAL PADE
>       &END XC_FUNCTIONAL
>     &END XC
>     &SCF
>       SCF_GUESS ATOMIC
>       EPS_SCF 1.0E-7
>       MAX_SCF 300
>       ADDED_MOS 10
>       &DIAGONALIZATION  ON
>         ALGORITHM STANDARD
>       &END DIAGONALIZATION
>       &MIXING  T
>         METHOD BROYDEN_MIXING
>         ALPHA 0.4
>         NBROYDEN 8
>       &END MIXING
>       &SMEAR ON
>         METHOD FERMI_DIRAC
>         ELECTRONIC_TEMPERATURE [K] 300
>       &END SMEAR
>     &END SCF
>   &END DFT
>   &PRINT
>     &FORCES ON
>     &END FORCES
>   &END PRINT
> &END FORCE_EVAL
>
> ***
>
> This also converges and yields a total energy E2=-34.555 a.u.
>
>
> Hence, my questions:
>
> 1. Is this even the correct way of calculating what I want, including the 
> energy calculations, XC functional, and basis?
> 2. Should the spin properties be explicitly set in the input? There are 
> none now.
> 3. Am I setting up the FCC lattice correctly (first input file)? My 
> translation vectors are set by the ABC values, but I have no idea whether 
> this is right.
> 4. If the first simulation yields the total energy of the system and the 
> FCC lattice implies 12 nearest neighbors, then removing the center would 
> change the total energy by (E1-E2)/6, which isn't the experimental -4.4 eV. 
> Am I completely off track here? :)
>
> Thanks a lot!
>
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