VASP Tutorial: A bit of surface science - NERSC

1 VASP Tutorial: A bit of surface scienceUniversity of Vienna,Faculty of Physics and Center for Computational Materials science ,Vienna, AustriaSetting up a VASP calculationVASP requires 4 input files to run a calculation: INCAR POSCAR KPOINTS POTCARI: The INCAR fileThe INCAR file contains the input parameters that steer the calculation: The default values set by VASP itself are a clever choice for moststandard calculations These standard settings may be modified to specify: What kind of calculation you want to do:SCF calculation, DOS, dielectric properties, .. Basic inputs concering the required precision, the requestedlevel of convergence, ..For a list of all INCAR-tags have a look at: The VASP manual: : The VASP wiki: : :INCARII: The POSCAR filefcc: NiHeader(comment) scaling (s)of atomic type(s)1 Number of atoms(of each type)Selective Dynamics(optional: selective dynamics)CartesianCartesian or Direct coordinates00 0 (T T T)positions of theatomsIn the POSCAR file you specify the structure (Bravaislattice and basis):III: The KPOINTS fileAutomaticmeshHeader(comment)0Nk=0:au tomatic mesh generationG (M) -centered(G) mesh or Monkhorst-Pack (M) grid4 4 4#of subdivisions along 0.

2 Shiftthe mesh ( )In the KPOINTS file you specify the points VASP will use to sample thefirst Brillouin zone in reciprocal spaceIV: The POTCAR fileThe POTCAR file has to contain the PAW datasets for all atomic types you havespecified in your POSCAR file:VASP comes with a library of PAW datasets, (one or more) for most elements of the periodic table: Each individual PAW data set starts with a descriptive section, specifying amongst other things: Parameters that were required to generate the dataset: Number of valence electrons Atomic mass Default energy cutoffs When your unit cell contains more than one type of atom you have to concatenate the corresponding PAW datasets in the same order as you havespecified the different atomic types in your POSCAR file. You should not mix PAW datasets generated with different exchange-correlation filesOUTCAR detailed output of a VASP run, including: a summary of the input parameters information about the individual electronic steps:total energy, Kohn-Sham eigenvalues, Fermi-energy.

3 Stress tensors forces in the atoms local charges, magnetic moments dielectric properties .. and a great many things more .. The amount of output written onto OUTCAR can be chosen by meansof the NWRITE-tag in the INCAR & stdout give a short summary of the self-consistency-cycle chosen SCF algorithm convergence of energy and charge density free energies, total magnetic moment of the cellOUTPUT filesCONTCAR& XDATCAR CONTCAR: updated geometry data at the end of a run lattice parameter Bravaismatrix ionic positions velocities the format of the CONTCAR is the same as for POSCAR:It can be directly be used for a continuation run (copy CONTCAR to POSCAR) XDATCAR: updated ionic positions of each ionic stepDOSCAR, CHGCAR & WAVECAR DOSCAR: total DOS andintegrated DOS, (local partial DOS) CHGCAR: the charge density WAVECAR: plane wavecoefficients of the be used to restart from a previous runDocumentation The VASP manual ( )Index: The VASP wiki ( )INCAR-tags.

4 INCARA bit of surface scienceExamples:Ni(100): surface relaxation surface energy LDOS surface bandstructureNi(111) cleansurface CO adsorption LDOS workfunction(change) frequenciesSTM ofgraphiteand grapheneNi(100) surface relaxation (ex.: Ni100clean_rel)POSCAR:fcc(100) surfaceHeader(comment) ..50000 ..00000 a(1)lattice vector a(2)lattice vector a(3)5 Number of atomsSelective DynamicsSwitch on selective dynamics CartesianPositions in .00000 .000000 F F .50000 .500000 F F .00000 F F .50000 T T .00000 T T Tpositions of the atoms, and thespecficationswhether or not theyare allowed to move during the relaxation. A (1 1) surface cell: 1 Ni atom per layer 5 Ni layers first two layers (on one side) are relaxed 3 vacuumPOTCAR:Ni GGA PAW potentialNi(100) surface relaxation (ex.: Ni100clean_rel)INCAR:SYTEM = cleanNi(100) surfaceNameof the calculationISTART= 0 ICHARG = 2initialwave functions: random numbersinitial charge density: overlapping atomsENCUT = 270cutoffenergy 270 eV (from POTCAR)ALGO = FastEDIFF = 1E-6use RMM-DIIS forelectronic optimizationelectronic convergence: energy change < 10-6eVISMEAR = 2 SIGMA = Methfessel-Paxtonsmearing (metal!)

5 Smearing width = = 2 MAGMOM = 5*1spin-polarizedcalculationinitial magnetic moment on each Ni = 1 IBRION = 1 NSW = 100 POTIM = relaxationKPOINTS:K-PointsHeader(comment )0Nk=0:automatic mesh generationMonkhorst-PackMonkhorst-Pack grid9 9 1#of subdivisions along (odd: centered on )0. shiftthe mesh ( ) 15 k-points in the IBZ 1 k-point along the z-direction!Ni(100) surface relaxation (ex.: Ni100clean_rel)Forces in the first and last step of the relaxation (in OUTCAR)POSITION TOTAL-FORCE (eV/Angst) drift: TOTAL-FORCE (eV/Angst) drift: (100) surface relaxation (ex.)

6 : Ni100clean_rel)Energy Convergence Energy changes during relaxationfrom eV to eV rel= 16meV surface energy: =12 surf atoms bulk surface energy of unrelaxed surface : unrel=12 5 = unrel+ rel= : you will find the setup for the calculation of the bulk energy in theNi100clean_ (EV)STEPSNi(100) surface relaxation (ex.: Ni100clean_rel)Start p4vasp:> p4v [ ]Step. 1) Go to:Convergence/EnergyStep. 2) update graphNi(100) surface relaxation (ex.: Ni100clean_rel)Final geometry from CONTCAR (or OUTCAR) file:fcc(100) F F F F F F T T T T +00 +00 + +00 +00 + +00 +00 + +00 +00 + +00 +00 +00 Inward/outward relaxation of the surface layers: 54= 100= 43= 100=+ (100) surface relaxation (ex.: Ni100clean_rel)Start p4vasp:> p4v [ ]Step 1.

7 Show structureStep 2.) Select initial or final positionsPossibly replicate cellsNi(100) LDOS (ex.: Ni100clean_LDOS)SYTEM = cleanNi(100) surfaceNameof the calculationENCUT = 270cutoffenergy 270 eV (from POTCAR)ALGO = Normaluse block-Davidsonfor electronic minimizationISMEAR = -5 Tetrahedron method with Bl chlcorrectionsISPIN = 2 MAGMOM = 5*1spin-polarizedcalculationinitial magnetic moment on each Ni = 1 LORBIT = 11LM-decomposedsite resolved density of : we want to use the optimized structure from Ni100clean_rel:Normally this would mean copying Ni100clean_rel/CONTCARtoPOSCAR in the directory where you want to run this case, however, that has already been taken care of, and thePOSCAR file in Ni100clean_LDOSis the correct (100) LDOS (ex.: Ni100clean_LDOS)total charge# of ion s p d tot------------------------------------- -----1 (x)# of ion s p d tot------------------------------------- -----1 At the end of the OUTCAR fileinformation on local charge andmagnetization is given.

8 Instead of LORBIT=11, one mightuse LORBIT=1and set RWIGS appropriately. As is clearly shown, the localmagnetic moments at thesurfaceare enhanced. The central layers behave bulk (100) LDOS (ex.: Ni100clean_LDOS) Projection onto surfaceand bulk layers. Each spin component isplotted separately. Band narrowing at thesurface. Exchange splitting islarger at the (100) LDOS (ex.: Ni100clean_LDOS)Select: Electronic/Local DOS+Bandscontrol Select atom,and orbital characterSelect spin channelInver y-axis (optional)Place pointer over atom, and press space to selection should appear in the Electronic Control applet above Press Show to show structureNi(100) surface bandstructure(ex.: Ni100clean_band)SYTEM = cleanNi(100) surfaceNameof the calculationENCUT = 270cutoffenergy 270 eV (from POTCAR)ALGO = Normaluse block-Davidsonfor electronic minimizationISMEAR = 2 SIGMA = Methfessel-Paxtonsmearing (metal!)

9 Smearing width = = 2 MAGMOM = 5*1spin-polarizedcalculationinitial magnetic moment on each Ni = 1 LORBIT = 11LM-decomposedsite resolved density of statesICHARG = 11 Readinitial charge from CHGCAR (ICHARG=1), and keep it fixed (ICHARG=ICHARG+10) during the subsequent : You need to copy the self-consistent charge density (CHGCAR) fromNi100clean_LDOSto the directory where you want to run need to do this: if VASP can not read the CHGCAR file, the run will (100) surface bandstructure(ex.: Ni100clean_band)kpointsfor band-structure .00000 .00000 .00000 .00000 .00000 .00000 .00000 .00000 .00000 .00000 .12500 .00000 .25000 .00000 .37500 .00000 .50000 .00000 .37500 .00000 .25000 .00000 .12500 .00000 .00000 .00000 1 KPOINTS: 13 k-points along X M Explicitly specfied, in reciprocalcoordinates All points with weight 1Ni(100) surface bandstructure(ex.)

10 : Ni100clean_band)Bandstructure (projected) calculationcharge density remains constant during runspin polarized status message in OUTCARon actual job: non-selfconsistent calc. Bandstructureconsist mainlyof bulk-like bands. Dots mark localization atsurface (100) surface bandstructure(ex.: Ni100clean_band)Place pointer over atom, and press space to selection should appear in the Electronic Control applet above Select: Electronic/Local DOS+Bandscontrol Select atom,and orbital characterPress Show to show structureSelect Bands Ni(111) surface relaxation (ex.: Ni111clean_rel)SYTEM = cleanNi(100) surfaceNameof the calculationISTART= 0 ICHARG = 2initialwave functions: random numbersinitial charge density: overlapping atomsENCUT = 270cutoffenergy 270 eV (from POTCAR)ALGO = FastEDIFF = 1E-6use RMM-DIIS forelectronic optimizationelectronic convergence: energy change < 10-6eVISMEAR = 2 SIGMA = Methfessel-Paxtonsmearing (metal!