Graphite interlayer distance: Difference between revisions
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In this example, dispersion correction method | In this example, dispersion correction method | ||
of Tchatchenko and Scheffler ( | of Tchatchenko and Scheffler (see {{TAG|Tkatchenko-Scheffler method}}) is used to cope with this problem. | ||
Optimal length of the lattice vector c normal to | Optimal length of the lattice vector c normal to | ||
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The computed value of 6.66 A agrees well with | The computed value of 6.66 A agrees well with | ||
experiment (6.71 A). | experiment (6.71 A). | ||
== Download == | == Download == | ||
[http://www.vasp.at/vasp-workshop/examples/graphiteDistance_ts.tgz graphiteDistance_ts.tgz] | [http://www.vasp.at/vasp-workshop/examples/graphiteDistance_ts.tgz graphiteDistance_ts.tgz] | ||
---- | ---- | ||
[[VASP_example_calculations|To the list of examples]] or to the [[The_VASP_Manual|main page]] | [[VASP_example_calculations|To the list of examples]] or to the [[The_VASP_Manual|main page]] | ||
[[Category:Examples]] | [[Category:Examples]] | ||
Revision as of 13:19, 10 May 2017
Task
Determine the interlayer distance of graphite in the stacking direction using the method of Tchatchenko and Scheffler to account for van der Waals interactions.
Input
POSCAR
graphite 1.0 1.22800000 -2.12695839 0.00000000 1.22800000 2.12695839 0.00000000 0.00000000 0.00000000 7.0 4 direct 0.00000000 0.00000000 0.25000000 0.00000000 0.00000000 0.75000000 0.33333333 0.66666667 0.25000000 0.66666667 0.33333333 0.75000000
INCAR
IVDW = 20 LVDW_EWALD =.TRUE. NSW = 1 IBRION = 2 ISIF = 4 PREC = Accurate EDIFFG = 1e-5 LWAVE = .FALSE. LCHARG = .FALSE. ISMEAR = -5 SIGMA = 0.01 EDIFF = 1e-6 ALGO = Fast NPAR = 2
KPOINTS
Monkhorst Pack 0 gamma 16 16 8 0 0 0
Calcualtion
Semilocal DFT at the GGA level underestimates long-range dispersion interactions. This problem causes a bad overestimation of graphite lattice in the stacking direction (8.84 A (PBE) vs. 6.71 A (exp)).
In this example, dispersion correction method of Tchatchenko and Scheffler (see Tkatchenko-Scheffler method) is used to cope with this problem.
Optimal length of the lattice vector c normal to the stacking direction is determined in a series of single point calculations with varied value of c (all other degrees of freedom are fixed at their experimental values).
The computed c vs. energy dependence is written in the file results.dat and can be visualized e.g. using xmgrace. The optimal value can be obtained using the attached utility (python with numpy or Numeric is needed):
./utilities/fit.py results.dat
200 iterations performed
Ch-square: 4.30305519481e-09
---------
E0(eV): -37.433456779
d0(A): 6.65603352689
The computed value of 6.66 A agrees well with experiment (6.71 A).
Download
To the list of examples or to the main page