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

Download

SiO2_NMR.tgz

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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