[Pw_forum] The overestimation of graphite lattice using vc-relax+vdW-DF

[WANG Wei]

Is it a bug? The optimized lattice constants of vdW-DF is so different from
those of vdw1, namely,

When I set input_dft       = 'vdw-DF', I got the


          total   stress  (Ry/bohr**3)                   (kbar)     P=
0.03
   0.00000033   0.00000000   0.00000000          0.05      0.00      0.00
   0.00000000   0.00000033   0.00000000          0.00      0.05      0.00
   0.00000000   0.00000000  -0.00000003          0.00      0.00      0.00

 CELL_PARAMETERS (alat=  4.68000000)
   1.000251032   0.000000003   0.000000000
  -0.500125514   0.866242806   0.000000000
   0.000000000   0.000000000   2.845991200


However,  I set input_dft       = 'vdw1', I got the

          total   stress  (Ry/bohr**3)                   (kbar)     P=
-0.01
  -0.00000002   0.00000000   0.00000000          0.00      0.00      0.00
   0.00000000  -0.00000002   0.00000000          0.00      0.00      0.00
   0.00000000   0.00000000  -0.00000007          0.00      0.00     -0.01

CELL_PARAMETERS (alat=  4.68000000)
   1.292794235  -0.000000090   0.000000000
  -0.646397196   1.119592604   0.000000000
   0.000000000   0.000000000   3.034982637
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