Bulk Nickel (and possibly other newbie questions)

Alex nedo... at gmail.com
Fri Aug 15 20:19:59 UTC 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
&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
&END XC_FUNCTIONAL
&END XC
&SCF
SCF_GUESS ATOMIC
EPS_SCF 1.0E-7
MAX_SCF 300
&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
&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
&END XC_FUNCTIONAL
&END XC
&SCF
SCF_GUESS ATOMIC
EPS_SCF 1.0E-7
MAX_SCF 300
&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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