Bulk Nickel (and possibly other newbie questions)

Alex nedo... at gmail.com
Fri Aug 15 22:19:59 CEST 2014


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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