Fermi-Dirac smearing and magnetism

[Marcella Iannuzzi]

Dear MP,

By increasing the temperature of the Fermi-Dirac smearing, more states get 
occupied and a different redistribution of electrons between the two spin 
channels is possible. I wouldn't call it an artefact, assuming that the 
distribution of states provided at this level of theory can be considered 
correct.
Just plot the PDOS at the different smearing temperatures to identify which 
are the responsible states for the behaviour that you are observing.

Kind regards,

Marcella



On Thursday, July 3, 2014 3:38:06 PM UTC+2, mpol wrote:
>
> Dear CP2k users,
>
>
> We try to model a semiconducting material (the gap is close to zero) with CP2k.
>
> The system has an even number of electrons and DFT-mGGA (TPSS functional with SR-MOLOPT-GTH BS
>
> and GTH pseudopotentials for PBE functional) is used to describe the electronic structure.
>
> It is practically impossible to converge the wavefunction of the system without smearing and thus
>
> Fermi-Dirac smearing is used. And here an interesting issue arises: when
> the smearing with electronic temperature of 1 K or 50 K is used, the
> system is paramagnetic. However when the smearing with electronic
> temperature of 300 K is used, the system becomes diamagnetic.
>
> May it be an artifact caused by smearing (so the system is truly
> paramagnetic at the room temperature) or it may be an evidence that the
> quenching of the magnetic moment occurs and the system is diamagnetic
> at the room temperature?
>
>
> With best regards,
>
> MP
>
>
> P.S. An example input file:
>
>
> &FORCE_EVAL
>   METHOD QS
>   &DFT
>     BASIS_SET_FILE_NAME [path]
>     POTENTIAL_FILE_NAME [path]
>     &MGRID
>       NGRIDS 5
>       CUTOFF 600
>       REL_CUTOFF 60
>     &END MGRID
>     &PRINT
>       &MO
> 	ADD_LAST SYMBOLIC
> 	COMMON_ITERATION_LEVELS 2000
> 	EIGENVALUES
> 	NDIGITS 8
> 	OCCUPATION_NUMBERS
> 	&EACH
> 	  GEO_OPT 1
> 	  QS_SCF 0
> 	&END EACH
>       &END MO
>     &END PRINT
>      UKS .TRUE.
>      MULTIP 1
>     &QS
>       EPS_DEFAULT 1.0E-14
>       METHOD GPW
>     &END QS
>     &POISSON
> 	PERIODIC XY
> 	PSOLVER ANALYTIC
>     &END POISSON
>     &SCF
>       EPS_EIGVAL 1.0E-10
>       SCF_GUESS RESTART
>       EPS_SCF 5.0E-06
>       MAX_SCF 300
>       &DIAGONALIZATION
>         ALGORITHM STANDARD
>         MAX_ITER 5
>       &END DIAGONALIZATION
>       &MIXING
> 	METHOD BROYDEN_MIXING
> 	NBUFFER 8
> 	ALPHA 0.2
> 	BETA 1.0
>       &END MIXING
>       &SMEAR
> 	METHOD FERMI_DIRAC
> 	ELECTRONIC_TEMPERATURE 300.0
>       &END SMEAR
>       ADDED_MOS 32
>     &END SCF
>     &XC
>       &XC_FUNCTIONAL TPSS
>       &END XC_FUNCTIONAL
>       &vdW_POTENTIAL
>          DISPERSION_FUNCTIONAL PAIR_POTENTIAL
>          &PAIR_POTENTIAL
>             TYPE DFTD3
>             PARAMETER_FILE_NAME [path]
>             REFERENCE_FUNCTIONAL TPSS
>             CALCULATE_C9_TERM .TRUE.
>             &PRINT_DFTD SILENT
> 	      COMMON_ITERATION_LEVELS 100
>             &END
>          &END PAIR_POTENTIAL
>       &END vdW_POTENTIAL
>     &END XC
>   &END DFT
>   &SUBSYS
>     &CELL
>     PERIODIC XY
>       ABC 19.64800 51.04800 16.00000
>        &END CELL
>     &TOPOLOGY
> 	&CENTER_COORDINATES .FALSE.
> 	&END
>     &END TOPOLOGY
>     &COORD
> [coords]
>     &END COORD
> [KIND sections with BSs and PPs specified in the message]
>   &END SUBSYS
> &END FORCE_EVAL
> &GLOBAL
>   RUN_TYPE GEO_OPT
>   PRINT_LEVEL MEDIUM
>   &TIMINGS
>      THRESHOLD 0.000001
>   &END
>   &DBCSR
>     MM_DRIVER BLAS
>   &END
> &END GLOBAL
> &MOTION
>     &GEO_OPT
> 	MAX_ITER 2000
>     &END
> &END
>
>
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