Alpha-SiO2: Difference between revisions
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*{{TAG|INCAR}} | *{{TAG|INCAR}} | ||
<pre> | <pre> | ||
SYSTEM = Si O2 | {{TAGBL|SYSTEM}} = Si O2 | ||
GGA = PE | {{TAGBL|GGA}} = PE | ||
ISTART = 1 | {{TAGBL|ISTART}} = 1 | ||
ICHARG = 0 | {{TAGBL|ICHARG}} = 0 | ||
INIWAV = 1 | {{TAGBL|INIWAV}} = 1 | ||
LREAL = AUTO | {{TAGBL|LREAL}} = AUTO | ||
ISYM = 2 | {{TAGBL|ISYM}} = 2 | ||
ISPIN = 1 | {{TAGBL|ISPIN}} = 1 | ||
Ionic minimisation | Ionic minimisation | ||
NSW = 0 | {{TAGBL|NSW}} = 0 | ||
ISIF = 2 | {{TAGBL|ISIF}} = 2 | ||
IBRION = 2 | {{TAGBL|IBRION}} = 2 | ||
# EDIFFG = -2E-2 | # {{TAGBL|EDIFFG}} = -2E-2 | ||
POTIM = 0.1 | {{TAGBL|POTIM}} = 0.1 | ||
Electronic minimisation | Electronic minimisation | ||
IALGO = 38 | {{TAGBL|IALGO}} = 38 | ||
LWAVE = .TRUE. | {{TAGBL|LWAVE}} = .TRUE. | ||
EMIN = -20.0 | {{TAGBL|EMIN}} = -20.0 | ||
EMAX = 10.0 | {{TAGBL|EMAX}} = 10.0 | ||
NEDOS = 1601 | {{TAGBL|NEDOS}} = 1601 | ||
EFG Calculation | EFG Calculation | ||
LEFG = .TRUE. | {{TAGBL|LEFG}} = .TRUE. | ||
QUAD_EFG = 0.0 25.5 | {{TAGBL|QUAD_EFG}} = 0.0 25.5 | ||
Chemical Shift | Chemical Shift | ||
PREC = Normal # nice | {{TAGBL|PREC}} = Normal # nice | ||
ENCUT = 400.0 # typically higher cutoffs than usual are needed | {{TAGBL|ENCUT}} = 400.0 # typically higher cutoffs than usual are needed | ||
ISMEAR = 0; SIGMA= 0.1 # no fancy smearings, SIGMA sufficiently small | {{TAGBL|ISMEAR}} = 0; SIGMA= 0.1 # no fancy smearings, SIGMA sufficiently small | ||
EDIFF = 1E-9 # you'd need much smaller EDIFFs. | {{TAGBL|EDIFF}} = 1E-9 # you'd need much smaller EDIFFs. | ||
LCHIMAG = .TRUE. # to switch on linear response for chemical shifts | {{TAGBL|LCHIMAG}} = .TRUE. # to switch on linear response for chemical shifts | ||
DQ = 0.001 # often the default is sufficient | {{TAGBL|DQ}} = 0.001 # often the default is sufficient | ||
ICHIBARE = 1 # often the default is sufficient | {{TAGBL|ICHIBARE}} = 1 # often the default is sufficient | ||
LNMR_SYM_RED = .TRUE. # be on the safe side | {{TAGBL|LNMR_SYM_RED}} = .TRUE. # be on the safe side | ||
NLSPLINE = .TRUE. # only needed if LREAL is NOT set. | {{TAGBL|NLSPLINE}} = .TRUE. # only needed if LREAL is NOT set. | ||
LREAL = A # helps for speed for large systems, not needed | {{TAGBL|LREAL}} = A # helps for speed for large systems, not needed | ||
NBANDS = 30 # to safe memory, ??? = NELECT/2 | {{TAGBL|NBANDS}} = 30 # to safe memory, ??? = NELECT/2 | ||
</pre> | </pre> | ||
Revision as of 13:39, 14 March 2017
Exercise : Determine the 17O Cq value and the Si and O schieldings.
α-SiO2 crystallizes in the trigonal P312 space group.
a = b = 4.604 Å; c = 5.207 Å
α = β = 90°; γ = 120°
The unit cell contains two independent atoms (1 Si and 1 O) with 3 formula units (SiO2) per unit cell (Z=3). SiO4 tetrahedron units are linked together by corner sharing.
In this exercise one wants first to calculate the EFG tensor components of 17O. This is very fast task calculated at the end of the first SCF calculation (ground state property). The experimental values for the Cq is 5.19 MHz. The nuclear quadrupolar momentum used to transform EFG in Cq is Q = 2.55 10-30 m2 (see the paper of Profeta et al. (http://pubs.acs.org/doi/abs/10.1021/ja027124r) (Silicon has a 1/2 nuclear spin, so Q is zero)
In a second step one wants to calculate the shielding parameters for Si and O. This is done using the linear response using the GIPAW formalism. As the calculation is quite time consuming, only very few k-points and small ENCUT are used with standard PAW data sets. The calculated shielding tensors components can be compared to the ones obtained by Profeta et al.
{{TAGBL|SYSTEM}} = Si O2 {{TAGBL|GGA}} = PE {{TAGBL|ISTART}} = 1 {{TAGBL|ICHARG}} = 0 {{TAGBL|INIWAV}} = 1 {{TAGBL|LREAL}} = AUTO {{TAGBL|ISYM}} = 2 {{TAGBL|ISPIN}} = 1 Ionic minimisation {{TAGBL|NSW}} = 0 {{TAGBL|ISIF}} = 2 {{TAGBL|IBRION}} = 2 # {{TAGBL|EDIFFG}} = -2E-2 {{TAGBL|POTIM}} = 0.1 Electronic minimisation {{TAGBL|IALGO}} = 38 {{TAGBL|LWAVE}} = .TRUE. {{TAGBL|EMIN}} = -20.0 {{TAGBL|EMAX}} = 10.0 {{TAGBL|NEDOS}} = 1601 EFG Calculation {{TAGBL|LEFG}} = .TRUE. {{TAGBL|QUAD_EFG}} = 0.0 25.5 Chemical Shift {{TAGBL|PREC}} = Normal # nice {{TAGBL|ENCUT}} = 400.0 # typically higher cutoffs than usual are needed {{TAGBL|ISMEAR}} = 0; SIGMA= 0.1 # no fancy smearings, SIGMA sufficiently small {{TAGBL|EDIFF}} = 1E-9 # you'd need much smaller EDIFFs. {{TAGBL|LCHIMAG}} = .TRUE. # to switch on linear response for chemical shifts {{TAGBL|DQ}} = 0.001 # often the default is sufficient {{TAGBL|ICHIBARE}} = 1 # often the default is sufficient {{TAGBL|LNMR_SYM_RED}} = .TRUE. # be on the safe side {{TAGBL|NLSPLINE}} = .TRUE. # only needed if LREAL is NOT set. {{TAGBL|LREAL}} = A # helps for speed for large systems, not needed {{TAGBL|NBANDS}} = 30 # to safe memory, ??? = NELECT/2
automatic mesh 0 Auto 20
O2 Si1 1.00000000000000 4.6040000915999997 0.0000000000000000 0.0000000000000000 -2.3020000457999998 3.9871810383000001 0.0000000000000000 0.0000000000000000 0.0000000000000000 5.2069997787000002 Si O 3 6 Direct 0.4436617824484789 -0.0000000000000000 0.3333333429999996 -0.0000000000000000 0.4436617824484789 0.6666666870000029 0.5563382175515210 0.5563382175515210 -0.0000000000000000 0.3926661416221499 0.3062177364999842 0.2428214976299141 0.6937822635000156 0.0864484051221655 0.5761548406299137 0.9135515948778347 0.6073338583778505 0.9094881546299145 0.3062177364999842 0.3926661416221499 0.7571785323700884 0.0864484051221655 0.6937822635000156 0.4238451593700863 0.6073338583778505 0.9135515948778347 0.0905118383700884
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Used INCAR Tags
DQ,EDIFF,EDIFFG,EMAX,EMIN,ENCUT,GGA,IALGO,IBRION,ICHARG,ICHIBARE,INIWAV,ISIF,ISMEAR,ISPIN,ISTART,ISYM,LCHIMAG,LEFG,LNMR_SYM_RED,LREAL,LWAVE,NBANDS,NEDOS,NLSPLINE,NSW,POTIM,PREC,QUAD_EFG,SYSTEM
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