Example: marketing

Hands on Session IV - VASP

Hands on Session IV. Martijn MARSMAN. Materialphysik and Center for Computational Material Science Institut fur Universit at Wien, Sensengasse 8/12, A-1090 Wien, Austria b-initio ackage ienna imulation M. M ARSMAN , H ANDS ON (4): MAGNETISM Page 1. Overview fcc Ni, an elementary ferromagnetic metal NiO, antiferromagnetic coupling LSDA+U (Dudarev's approach). SOI: freestanding fcc Fe and Ni (100) monolayers Constraining magnetic moments What to do about convergence problems? M. M ARSMAN , H ANDS ON (4): MAGNETISM Page 2. fcc Ni POSCAR. fcc: . Volume set to A. fcc primitive cell 1 KPOINTS. Cartesian 11 11 11 -centered .. 0 0 0. Monkhorst-Pack grid POTCAR. k-points 0 makepaw_GGA Ni Gamma (a PAW-GGA PW91 potential). 11 11 11. 0 0 0. M. M ARSMAN , H ANDS ON (4): 4 1 N I Page 3. INCAR. SYSTEM = Ni fcc bulk ISTART = 0 Spin polarized calculation (collinear). ISPIN = 2. MAGMOM = Initial magnetic moment: 1 B. ISMEAR = -5 Interpolation of the correlation part of VOSKOWN = 1.

Hands on Session IV Martijn MARSMAN Institut fur¨ Materialphysik and Center for Computational Material Science Universitat¨ Wien, Sensengasse 8/12, A-1090 Wien, Austria

Tags:

  Sessions, Hands, Hands on session iv

Information

Domain:

Source:

Link to this page:

Please notify us if you found a problem with this document:

Other abuse

Transcription of Hands on Session IV - VASP

1 Hands on Session IV. Martijn MARSMAN. Materialphysik and Center for Computational Material Science Institut fur Universit at Wien, Sensengasse 8/12, A-1090 Wien, Austria b-initio ackage ienna imulation M. M ARSMAN , H ANDS ON (4): MAGNETISM Page 1. Overview fcc Ni, an elementary ferromagnetic metal NiO, antiferromagnetic coupling LSDA+U (Dudarev's approach). SOI: freestanding fcc Fe and Ni (100) monolayers Constraining magnetic moments What to do about convergence problems? M. M ARSMAN , H ANDS ON (4): MAGNETISM Page 2. fcc Ni POSCAR. fcc: . Volume set to A. fcc primitive cell 1 KPOINTS. Cartesian 11 11 11 -centered .. 0 0 0. Monkhorst-Pack grid POTCAR. k-points 0 makepaw_GGA Ni Gamma (a PAW-GGA PW91 potential). 11 11 11. 0 0 0. M. M ARSMAN , H ANDS ON (4): 4 1 N I Page 3. INCAR. SYSTEM = Ni fcc bulk ISTART = 0 Spin polarized calculation (collinear). ISPIN = 2. MAGMOM = Initial magnetic moment: 1 B. ISMEAR = -5 Interpolation of the correlation part of VOSKOWN = 1.

2 The exchange-correlation functional LORBIT = 11. according to: Or copy the files from: S. H. Vosko, L. Wilk and M. Nusair, Can. J. Phys. 58, 1200 (1980). vw/4_1_Ni k-mesh integration: tetrahedron method with Bl ochl's correc- tions Orbital resolved DOS. and calculation of local magnetic moment M. M ARSMAN , H ANDS ON (4): 4 1 N I Page 4. The magnetic moment In OSZICAR (total magnetic moment): N E dE d eps ncg rms rms(c). DAV: 1 +02 +02 +03 2338 +02. DAV: 2 +01 +02 +02 2282 +02. DAV: 3 +01 +00 +00 2536 +01. DAV: 4 +01 2344 DAV: 5 +01 1832 +00.. DAV: 9 +01 2946 DAV: 10 +01 1364 1 F= +01 E0= +01 d E = +00 mag= in OUTCAR (integration of magnetic moment in the PAW sphere): magnetization (x). # of ion s p d tot ---------------------------------------- 1 M. M ARSMAN , H ANDS ON (4): 4 1 N I Page 5. DOS. fcc Ni 3. n(E) (states/eV atom). 2. 1. 0. 1. 2. 3. 4 2 0 2 4 6. E(eV). Exchange splitting eV.. M. M ARSMAN , H ANDS ON (4): 4 1 N I Page 6.

3 Proper initialization of magnetic moment Too small initial moment will/may lead to a nonmagnetic solution (the previous example with MAGMOM = ).. DAV: 9 +01 2091 DAV: 10 +01 1059 1 F= +01 E0= +01 d E = +00 mag= Badly initialized calculations take longer to converge Coexistence of low- and high spin solutions M. M ARSMAN , H ANDS ON (4): 4 1 N I Page 7. Noncollinear magnetism Replace ISPIN = 2 and MAGMOM = by: LNONCOLLINEAR = .TRUE. MAGMOM = leads to DAV: 9 +01 7532 DAV: 10 +01 4328 1 F= +01 E0= +01 d E = +00 mag= or with MAGMOM = DAV: 9 +01 7548 DAV: 10 +01 4288 1 F= +01 E0= +01 d E = +00 mag= idem for MAGMOM = DAV: 9 +01 7552 DAV: 10 +01 4292 1 F= +01 E0= +01 d E = +00 mag= M. M ARSMAN , H ANDS ON (4): 4 1 N I Page 8. NiO. Rocksalt structure AFM ordering of Ni (111) planes M. M ARSMAN , H ANDS ON (4): 4 2 N I O Page 9. POSCAR. NiO AFM. AFM coupling: 4 atoms in the basis (instead of 2). KPOINTS. 2 2. Cartesian 4 4 4 -centered.

4 Monkhorst-Pack grid POTCAR. makepaw Ni O_s k-points (PAW-LDA potentials). 0. Gamma 4 4 4. 0 0 0. M. M ARSMAN , H ANDS ON (4): 4 2 N I O Page 10. INCAR. SYSTEM = NiO. Initial magnetic moment: ISPIN = 2 2 B (Ni), 0 B (O).. MAGMOM = 2*0. AMIX= and AMIX MAG= (default). ENMAX = 250 BMIX and BMIX MAG practically zero, EDIFF = 1E-3. linear mixing ISMEAR = -5. Or copy the files from: AMIX = BMIX = vw/4_2_NiO. AMIX_MAG = BMIX_MAG = LORBIT = 11. M. M ARSMAN , H ANDS ON (4): 4 2 N I O Page 11. The magnetic moment In OSZICAR (total magnetic moment = 0!): N E dE d eps ncg rms rms(c).. DAV: 13 +02 552 DAV: 14 +02 520 1 F= +02 E0= +02 d E = +00 mag= in OUTCAR (integration of magnetic moment in the PAW sphere): magnetization (x). # of ion s p d tot ---------------------------------------- 1 2 3 4 ---------------------------------------- -------- tot M. M ARSMAN , H ANDS ON (4): 4 2 N I O Page 12. Total DOS, and LDOS Ni d-orbitals DOS Ni d LDOS.

5 8. 4 t2g 6. n(E) (states/eV atom). n(E) (states/eV atom). eg 4. 2. 2. 0 0. 2. 2. 4. 6 4. 8. 4 2 0 2 4 6 8 10 4 2 0 2 4 6 8 10. E(eV) E(eV). mNi = B (exp. B ) Egap = eV (exp. eV).. M. M ARSMAN , H ANDS ON (4): 4 2 N I O Page 13. LSDA+U; Dudarev's approach .. addition to INCAR of NiO calc. LDAU = .TRUE. Switch on L(S)DA+U. LDAUTYPE = 2. LDAUL = 2 -1 Select Dudarev's approach LDAUU = 8 00 (LSDA+U Type 2). LDAUJ = LDAUPRINT = 2 L quantum number for which on site interac- tion is added Or copy the files from: (-1 = no on site interaction). vw/4_3_NiO_LSDA+U U parameter J parameter Print occupation matrices in OUTCAR. L,U, and J must be specified for all atomic types! M. M ARSMAN , H ANDS ON (4): 4 3 N I O LSDA+U Page 14. On site occupancies (see OUTCAR). atom = 1 type = 1 l = 2. onsite density matrix .. occupancies and eigenvectors o = v = o = v = o = v = o = v = o = v = o = v = o = v = o = v = o = v = o = v = dxy dyz d z2 dxz dx2 dxy dyz dz2 dxz dx2.

6 R2 y2 r2 y2.. M. M ARSMAN , H ANDS ON (4): 4 3 N I O LSDA+U Page 15. For comparison: when U=0 and J=0 ( just LSDA) the on site occupancies are as follows: o = v = o = v = o = v = o = v = o = v = o = v = o = v = o = v = o = v = o = v = dxy dyz d z2 dxz dx2 dxy dyz dz2 dxz dx2.. r2 y2 r2 y2.. M. M ARSMAN , H ANDS ON (4): 4 3 N I O LSDA+U Page 16. The Ni d-LDOS and local magnetic moment LSDA Dudarev U=8 J= 4 t2g 4 t2g n(E) (states/eV atom). n(E) (states/eV atom). eg eg 2 2. 0 0. 2 2. 4 4. 4 2 0 2 4 6 8 10 4 2 0 2 4 6 8 10. E(eV) E(eV). magnetization (x). # of ion s p d tot ---------------------------------------- 1 2 3 4 ---------------------------------------- -------- tot M. M ARSMAN , H ANDS ON (4): 4 3 N I O LSDA+U Page 17. Total Energy On site occupancy matrix is NOT idempotent . Total energy contains penalty contribution! .. DAV: 15 +02 520 DAV: 16 +02 520 1 F= +02 E0= +02 d E = +00 mag= The total energy for U J 0 is in that case always higher than for U J 0.

7 (just LSDA, see below): .. DAV: 13 +02 552 DAV: 14 +02 520 1 F= +02 E0= +02 d E = +00 mag= Comparing the total energies from calculations with different U J is meaningless! . M. M ARSMAN , H ANDS ON (4): 4 3 N I O LSDA+U Page 18. SOI: freestanding fcc Fe and Ni (100) monolayers POSCAR. fcc Ni (100) monolayer Lattice constant for bulk fcc Ni .50000 .50000 .00000 (for Fe take a0 3 45 A) ..50000 .00000..00000 .00000 POTCAR. 1. Cartesian makepaw_GGA Ni .00000 .00000 .00000 or makepaw_GGA Fe K-Points 0. Monkhorst-Pack 9 9 1. 0 0 0. M. M ARSMAN , H ANDS ON (4): 4 4 SOI N I AND 4 4 SOI F E Page 19. INCAR. ISTART = 0. ENCUT = Initialize moment along z-direction LNONCOLLINEAR = .TRUE. (out of plane). MAGMOM = VOSKOWN = 1. For Fe: MAGMOM = LSORBIT = .TRUE. Switch on Spin-Orbit Interaction For the second calculation, switch to in-plane magnetization, setting MAGMOM = (for Fe: MAGMOM = ). Input files can be found in: vw/4_4_SOI_Ni and vw/4_4_SOI_Fe M.

8 M ARSMAN , H ANDS ON (4): 4 4 SOI N I AND 4 4 SOI F E Page 20. Results fcc Ni (100) monolayer (out of plane magnetization).. DAV: 20 +01 636 DAV: 21 +01 500 1 F= +01 E0= +01 d E = mag= fcc Ni (100) monolayer (in plane magnetization).. DAV: 19 +01 1084 DAV: 20 +01 916 1 F= +01 E0= +01 d E = mag= EMAE E m E m 1 2 meV (easy axis lies in plane).. For Fe the same procedure yields EMAE E m E m 0 2 meV (easy axis lies out of plane).. M. M ARSMAN , H ANDS ON (4): 4 4 SOI N I AND 4 4 SOI F E Page 21. Constraining the direction of magnetic moments POSCAR. Fe dimer An iron dimer in a box KPOINTS. 2. Cartesian We only take the point POTCAR. k-points makepaw_GGA Fe 0. Gamma 1 1 1 Or copy the files from: 0 0 0 vw/4_5_Fe_dimer M. M ARSMAN , H ANDS ON (4): 4 5 F E DIMER Page 22. INCAR. ISTART = 0. ISYM = 0 Switch of symmetry LNONCOLLINEAR = .TRUE. MAGMOM = 0 0 3 0 0 3 Initialize moments for VOSKOWN = 1 ferromagnetic coupling LORBIT = 11.

9 DAV: 20 +01 60 DAV: 21 +01 60 1 F= +01 E0= +01 d E = mag= Now take MAGMOM = 0 0 3 0 2 2. magnetization (y) magnetization (z). # of ion s p d tot # of ion s p d tot ---------------------------------------- ---------------------------------------- 1 1 2 2 ---------------------------------------- ---------------------------------------- tot tot System converges to FM solution M. M ARSMAN , H ANDS ON (4): 4 5 F E DIMER Page 23. However when we add the following lines to the INCAR. I_CONSTRAINED_M = 1. RWIGS = Switch on constraints LAMBDA = 10 on magnetic moments M_CONSTR = 0 0 1 0 1 1. Integration radius to determine local moments Weight in penalty functional Target directions a penalty functional is added to the system which drives the integrated local moments into the desired directions. Beware: The penalty functional contributes to the total energy M. M ARSMAN , H ANDS ON (4): 4 5 F E DIMER Page 24. The necessary information is found in the OSZICAR: E_p = lambda = +02.

10 Ion MW_int M_int 1 2 DAV: 35 +01 60 1 F= +01 E0= +01 d E = mag= E p is the energy arising from the penalty functional It decreases with increasing LAMBDA! By increasing LAMBDA stepwise one can bring E p down (slowly so the solution remains stable from one run to another). E_p = lambda = +02. ion MW_int M_int 1 2 DAV: 33 +01 60 1 F= +01 E0= +01 d E = mag= This way one approaches the LSDA total energy for a given magnetic configuration M. M ARSMAN , H ANDS ON (4): 4 5 F E DIMER Page 25. What can one do when convergence is bad? Start from charge density of non-spin-polarized calculation, using ISTART = 0 (or remove WAVECAR). ICHARG = 1. Linear mixing BMIX = ; BMIX MAG = Mix slowly, , reduce AMIX and AMIX MAG. Reduce MAXMIX, the number of steps stored in the Broyden mixer (default = 45). Restart from partly converged results (stop a calculation after say 20 steps and restart from the WAVECAR). Use constraints to stabilize the magetic configuration Pray M.


Related search queries