some questions about Adsorption energy of Nickel atom/cluster on oxide surfaces

[Amin]

Hi folks,

I'm new to CP2K and I want to measure adsorption energy of Ni atom (in 
further steps, cluster) on some oxide surfaces. Here are my questions:

1. When I try to calculate Energy of single Ni atom in gas phase by using 
Diagonalization method, it works with MULTIPLICITY 1, but once I set the 
MULTIPLICITY to 3, it doesn't converge. (Please check my input file below). 
I was wondering what's the reason for that? and how can I overcome this 
problem.

2. Is that reliable to calculate the energy of Ni atom/cluster with 
Diagonalization but the energy of complex (Ni on oxide surface) with OT and 
then compare them together to achieve the adsorption energy of metal? Do I 
need to use same method for all of the calculations? even if there is just 
one single Ni atom adsorbed on the surface? 

3. the same question for POISSON_SOLVER: is that OK to use different 
Poisson solvers for metal atom/cluster and the complex? or again I need to 
use the same solvers to achieve the correct amount for adsorption energy?

I would highly appreciate your advises.

P.S:Here is my input file for the calculation of single Ni atom:
&GLOBAL
  PROJECT  m-Ni
  RUN_TYPE GEO_OPT
  PRINT_LEVEL LOW
  EXTENDED_FFT_LENGTHS
&END GLOBAL

&FORCE_EVAL
  METHOD Quickstep             
  &DFT
    BASIS_SET_FILE_NAME ./BASIS_MOLOPT
    POTENTIAL_FILE_NAME ./GTH_POTENTIALS
    UKS
    MULTIPLICITY 3
    &MGRID
CUTOFF 800
REL_CUTOFF 60
    &END MGRID
    &QS
METHOD GPW
EPS_DEFAULT 1.0E-12
    &END QS
    &POISSON
PERIODIC XY
        POISSON_SOLVER MT
    &END POISSON
     &SCF
     SCF_GUESS  ATOMIC
     EPS_SCF 1.0E-6
     MAX_SCF 500
     ADDED_MOS  20
     CHOLESKY INVERSE
     &SMEAR  ON
         METHOD FERMI_DIRAC
         ELECTRONIC_TEMPERATURE [K] 300
     &END SMEAR
     &DIAGONALIZATION
          ALGORITHM STANDARD
     &END DIAGONALIZATION
     &MIXING
          METHOD BROYDEN_MIXING
          ALPHA   0.1
          BETA    1.5
          NBROYDEN  8
     &END MIXING
     &PRINT
&RESTART
&EACH
QS_SCF 100
&END
ADD_LAST NUMERIC
        &END
     &END PRINT
    &END SCF
    &XC                       
      &XC_FUNCTIONAL PBE
      &END XC_FUNCTIONAL
      &VDW_POTENTIAL
DISPERSION_FUNCTIONAL PAIR_POTENTIAL
&PAIR_POTENTIAL
TYPE DFTD3(BJ)
REFERENCE_FUNCTIONAL PBE
CALCULATE_C9_TERM .FALSE.
PARAMETER_FILE_NAME ./dftd3.dat
R_CUTOFF 15.0
&END PAIR_POTENTIAL
      &END VDW_POTENTIAL
    &END XC
  &END DFT

  &SUBSYS
    &CELL
      A 11.35350 0.00000 0.00000
      B -5.67675 15.1390 0.00000
      C 0.000000 0.00000 30.0000
      PERIODIC XY
    &END CELL
    &COORD
        @INCLUDE 'Ni.coord'
    &END COORD
    &KIND C
      ELEMENT C
      BASIS_SET TZVP-MOLOPT-GTH
      POTENTIAL GTH-PBE-q4
    &END KIND
    &KIND Ni
      ELEMENT Ni
      BASIS_SET DZVP-MOLOPT-SR-GTH
      POTENTIAL GTH-PBE-q18
    &END KIND
    &KIND O
      ELEMENT O
      BASIS_SET TZVP-MOLOPT-GTH
      POTENTIAL GTH-PBE-q6
    &END KIND
  &END SUBSYS
  &PRINT
&TOTAL_NUMBERS ON
&END TOTAL_NUMBERS
  &END PRINT
&END FORCE_EVAL
&MOTION
&GEO_OPT
 OPTIMIZER BFGS
 MAX_FORCE 4.500E-004
&END
&END MOTION

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