CRYSTAL
 PRIMVEC
   -2.698803764    0.000000000    2.698803764
    0.000000000    2.698803764    2.698803764
   -2.698803764    2.698803764    0.000000000
 PRIMCOORD
           2           1
Si        0.000000000    0.000000000    0.000000000
Si        1.349401882    1.349401882    1.349401882
BEGIN_BLOCK_DATAGRID_3D
3D_PWSCF
DATAGRID_3D_UNKNOWN
          56          40          40
  0.000000  0.000000  0.000000
  5.397608  5.397608  0.000000
  0.000000  0.000000  5.397608
-10.795215  5.397608  0.000000

[...]
[here the 3d grid data for charge density  ] 
 [...]
END_DATAGRID_3D
END_BLOCK_DATAGRID_3D