Alpha-SiO2: Difference between revisions

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The calculated shielding tensors components can be compared to the ones obtained by Profeta ''et al.''
The calculated shielding tensors components can be compared to the ones obtained by Profeta ''et al.''


*INCAR
*{{TAG|INCAR}}
<pre>
  SYSTEM      = Si O2


   GGA          = PE
   {{TAGBL|SYSTEM}}      = Si O2
   ISTART      = 1
  {{TAGBL|GGA}}         = PE
   ICHARG      = 0
   {{TAGBL|ISTART}}       = 1
   INIWAV      = 1
   {{TAGBL|ICHARG}}       = 0
   LREAL        =  AUTO
   {{TAGBL|INIWAV}}       = 1
   ISYM        = 2
   {{TAGBL|LREAL}}       =  AUTO
   ISPIN        = 1
   {{TAGBL|ISYM}}         = 2
   {{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
 
   {{TAGBL|LWAVE}}       = .TRUE.
   LWAVE        = .TRUE.
   {{TAGBL|EMIN}}         =  -20.0
 
   {{TAGBL|EMAX}}         =  10.0
   EMIN        =  -20.0
   {{TAGBL|NEDOS}}       = 1601
   EMAX        =  10.0
   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.
  {{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


  LCHIMAG      = .TRUE.  # to switch on linear response for chemical shifts
  DQ          = 0.001        # often the default is sufficient
  ICHIBARE    = 1      # often the default is sufficient
  LNMR_SYM_RED = .TRUE. # be on the safe side
  NSLPLINE    = .TRUE.  # only needed if LREAL is NOT set.
  LREAL        = A          # helps for speed for large systems, not needed
  NBANDS      = 30      # to safe memory, ??? = NELECT/2
</pre>


*KPOINTS
*{{TAG|KPOINTS}}
<pre>
<pre>
automatic mesh
automatic mesh
Line 74: Line 70:
</pre>
</pre>


*POSCAR
*{{TAG|POSCAR}}
<pre>
<pre>
O2 Si1
O2 Si1
Line 96: Line 92:


== Download ==
== Download ==
[http://www.vasp.at/vasp-workshop/examples/SiO2_NMR.tgz SiO2_NMR.tgz]
[[Media:SiO2_NMR.tgz| SiO2_NMR.tgz]]


----
----
[[VASP_example_calculations|To the list of examples]] or to the [[The_VASP_Manual|main page]]


[[Category:Examples]]
[[Category:Examples]]

Latest revision as of 13:16, 14 November 2019

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.

 SYSTEM      = Si O2
 GGA          = PE
 ISTART       = 1
 ICHARG       = 0
 INIWAV       = 1
 LREAL        =  AUTO
 ISYM         = 2
 ISPIN        = 1

Ionic minimisation

 NSW          = 0
 ISIF         = 2
 IBRION       = 2
  1. EDIFFG = -2E-2
 POTIM        = 0.1

Electronic minimisation

 IALGO        = 38
 LWAVE        = .TRUE.
 EMIN         =   -20.0
 EMAX         =   10.0
 NEDOS        = 1601

EFG Calculation

 LEFG         = .TRUE.
 QUAD_EFG     = 0.0 25.5

Chemical Shift

 PREC         = Normal    # nice
 ENCUT        = 400.0      # typically higher cutoffs than usual are needed
 ISMEAR = 0; SIGMA= 0.1 # no fancy smearings, SIGMA sufficiently small
 EDIFF        = 1E-9      # you'd need much smaller EDIFFs.
 LCHIMAG      = .TRUE.   # to switch on linear response for chemical shifts
 DQ           = 0.001         # often the default is sufficient
 ICHIBARE     = 1       # often the default is sufficient
 LNMR_SYM_RED = .TRUE. # be on the safe side
 NLSPLINE     = .TRUE.  # only needed if LREAL is NOT set.
 LREAL        = A          # helps for speed for large systems, not needed
 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