Electron poor materials research group Group meeting Dec 16, 2010 Theory- PAW_PBE psuedo potentials. EOS relaxations and bader analysis of resultant structures.

System’s under study  Electron Poor Materials  ZnSb  ZnAs  Li 2 Sb  Mg 3 Sb 2  Tetrahedral, sp 3 systems  InSb  GaSb  ZnSe  ZnTe  GaAs  Si

Procedure  Very accurate EOS relaxations were preformed.  The system cell shape and volume was relaxed while the volume was kept fixed to give a point in the EOS curve.  A final relaxation was performed to bring the system to the target volume given by the Birch- Murnaghan EOS.  From the final relaxation a static calculation was performed to get the charge densities for Bader analysis.  Bader analysis was performed on the charge densities from the static run.

Example INCAR for EOS relaxation. System = InSb NSW = 5 | number of ionic steps ISIF = 4 | ISIF=4 relax cellshape and ions. NOT volume IBRION = 1 | ionic relaxation algorithm EDIFF = 1E-5 | break condition for elec. SCF loop EDIFFG = -1E-4 | break condition for ionic relaxation loop MAXMIX = 80 | keep dielectric function between ionic movements NELMIN = 6 | minimum number of electronic steps NFREE = 15 | number of degrees of freedom (don't go above 20) #RECOMMENDED MINIMUM SETUP #GGA= #xchange-correlation #VOSKOWN= #=1 if GGA=91; else = 0 PREC = ACCURATE #PRECISION, sets fft grid ENCUT = 225 #energy cutoff, commented to use enmax in potcar LREAL =.FALSE. #.FALSE. MEANS USE RECIPROCAL LATTICE ISMEAR = 0 #0 means use gaussian smearing It should be noted that not all relaxations have the same VASP setup as I had difficulties with some of the systems crashing in VASP with very accurate relaxation parameters. This was machine independent.

Example INCAR for EOS static. System = InSb #ISTART = 0 # startjob: no WAVECAR file #ICHARGE = 2 # charge: from atoms #INIWAV = 1 # random initialization for wf. NELM = 40 # maximum of 40 electronic steps NELMIN = 4 # minimum of 2 steps NELMDL = -5 # no update of charge for 3 steps EDIFF = 1E-5 # accuracy for electronic minimization #RECOMMENDED MINIMUM SETUP #GGA= #xchange-correlation #VOSKOWN= #=1 if GGA=91; else = 0 PREC = ACCURATE #PRECISION, sets fft grid ENCUT = 225 #energy cutoff, commented to use enmax in potcar LREAL =.FALSE. #.FALSE. MEANS USE RECIPROCAL LATTICE ISMEAR = -5 #-5 means use tetrahedral with blochl It should be noted that not all relaxations have the same VASP setup as I had difficulties with some of the systems crashing in VASP with very accurate relaxation parameters. This was machine independent.

INCAR For final relaxation calculations System = InSb relaxsetup.sh NSW = 20 | number of ionic steps ISIF = 4 | (ISIF=2 Relax ions only, ISIF=3 Relax everything) IBRION = 1 | ionic relaxation algorithm EDIFF = 1E-9 | break condition for elec. SCF loop EDIFFG = -1E-8 | break condition for ionic relaxation loop MAXMIX = 80 | keep dielectric function between ionic movements NELMIN = 8 | minimum number of electronic steps NFREE = 20 | number of degrees of freedom (don't go above 20) #RECOMMENDED MINIMUM SETUP #GGA= #xchange-correlation #VOSKOWN= #=1 if GGA=91; else = 0 PREC = ACCURATE #PRECISION, sets fft grid ENCUT = 225 #energy cutoff, determines number of lattice vectors LREAL =.FALSE. #.FALSE. MEANS USE RECIPROCAL LATTICE ISMEAR = 0 #determines how partial occupancies a set.

INCAR For final static calculations System = InSb SIGMA = 0.01 #RECOMMENDED MINIMUM SETUP PREC = ACCURATE #PRECISION ENCUT = 225 LREAL =.FALSE. #.FALSE. MEANS USE RECIPROCAL LATTICE ISMEAR = 0 #USE GAUSSIAN SMEARING #FOR GW CALCULATIONS #LOPTICS =.TRUE. #NBANDS = 96 #FOR BADER ANALYSIS LAECHG=.TRUE. NGXF = 126 #USE 6X NGX for bader analysis NGYF = 126 NGZF = 126

The equations of state for the 10 materials are below. Equations of State % differences are caluclated via:

Exp Vol: PAW_PBE Vol: 73.48

Exp Vol: PAW_PBE Vol: 60.31

Exp Vol: PAW_PBE Vol: 47.35

Exp Vol: PAW_PBE Vol: 59.17

Exp Vol: PAW_PBE Vol: lat constant:

Exp Vol: PAW_PBE Vol: 40.89

Exp Vol: PAW_PBE Vol:

Exp Vol: PAW_PBE Vol:

Exp Vol: PAW_PBE Vol:

Exp Vol: PAW_PBE Vol:

Li 2 Sb EOS troubles.  The above graph is the ugliest out of the set which makes me worry about the results for this structure.  I have tried changing psuedo-potentials to include more core electrons (currently there is only 1 valence electron in the calculation).  this however has crashed in the relaxation step I believe due to the large number of plane waves needed. ENMAX in POTCAR is 650 eV for Li_pv.  It is not uncommon for VASP to in relaxation on these larger systems if the plane waves gets too big or the precision flag is set too high. This is machine independent.

Equation of State Results. Structure Name Exp. Vol (Ang^3) VASP Vol (Ang^3)%diff InSb GaSb ZnSe ZnTe GaAs Si ZnSb ZnAs Mg3Sb Li2Sb

bader analysis of the structures that were relaxed from the target volume of the EOS calculations above. Bader analysis

InSbACF.dat # X Y Z CHARGE MIN DIST ATOMIC VOL VACUUM CHARGE: VACUUM VOLUME: NUMBER OF ELECTRONS: Charge Transfer:

GaSbACF.dat # X Y Z CHARGE MIN DIST ATOMIC VOL VACUUM CHARGE: VACUUM VOLUME: NUMBER OF ELECTRONS: Charge Transfer:

ZnSeACF.dat # X Y Z CHARGE MIN DIST ATOMIC VOL VACUUM CHARGE: VACUUM VOLUME: NUMBER OF ELECTRONS: Charge Transfer:

ZnTeACF.dat # X Y Z CHARGE MIN DIST ATOMIC VOL VACUUM CHARGE: VACUUM VOLUME: NUMBER OF ELECTRONS: Charge Transfer:

GaAsACF.dat # X Y Z CHARGE MIN DIST ATOMIC VOL VACUUM CHARGE: VACUUM VOLUME: NUMBER OF ELECTRONS: Charge Transfer:

SiACF.dat # X Y Z CHARGE MIN DIST ATOMIC VOL VACUUM CHARGE: VACUUM VOLUME: NUMBER OF ELECTRONS: Charge Transfer:

ZnSbACF.dat # X Y Z CHARGE MIN DIST ATOMIC VOL VACUUM CHARGE: VACUUM VOLUME: NUMBER OF ELECTRONS: Charge Transfer:

ZnAsACF.dat # X Y Z CHARGE MIN DIST ATOMIC VOL VACUUM CHARGE: VACUUM VOLUME: NUMBER OF ELECTRONS: Charge Transfer:

Mg 3 Sb 2 ACF.dat # X Y Z CHARGE MIN DIST ATOMIC VOL VACUUM CHARGE: VACUUM VOLUME: NUMBER OF ELECTRONS: Charge Transfer:

Li 2 SbACF.dat # X Y Z CHARGE MIN DIST ATOMIC VOL VACUUM CHARGE: VACUUM VOLUME: NUMBER OF ELECTRONS: Charge Transfer:

Bader Analysis results Crystal Name Bader charge transfer Pauling Electronegativity Philips Ionicity 1 Si ZnSb GaSb InSb ZnAs ZnTe GaAs ZnSe Li2Sb Mg3Sb ) Phillips. Rev. Mod. Phys. 42, 3, 1970