[Spglib-users] spglib and cubic silicon

[SAYEDE A. <say...@ho...>]

Dear spglib devlopper and users,
I wanted a clarification on the use of spglib in the case of cubic silicon, I want to find the primitive cell of the following structure 
Lattice:4.000000 0.000000 0.0000000.000000 4.000000 0.0000000.000000 0.000000 4.000000
Positions :0.000000 0.000000 0.0000000.250000 0.750000 0.7500000.000000 0.500000 0.5000000.250000 0.250000 0.2500000.500000 0.000000 0.5000000.750000 0.750000 0.2500000.500000 0.500000 0.0000000.750000 0.250000 0.750000
spg_find_primitive give me :
Lattice:2.000000 -2.000000 2.000000-2.000000 -0.000000 2.0000000.000000 -2.000000 0.000000
Positions :0.000000 0.000000 0.000000-0.250000 -0.500000 0.250000
When I use the obtained structure spg_get_dataset indicate that structure has  Cm (8) symmetry !!
The code : #######################################################################################include "spglib.h"#include <stdio.h>
int main(){  double lattice[3][3] = { {4, 0, 0}, {0, 4, 0}, {0, 0, 4} };  double positions[32][3];  double pos_orig[][3] = {    {0, 0, 0},    {0.0, 0.5, 0.5},    {0.5, 0.5, 0.0},    {0.5, 0.0, 0.5},    {0.75, 0.25, 0.75},    {0.25, 0.25, 0.25},    {0.25, 0.75, 0.75},    {0.75, 0.75, 0.25}  };  int types[32];  int i, num_atom = 8, num_atom_prim, num_atom_bravais;  double symprec = 1e-5;
  for (i = 0; i < num_atom; i++) {    positions[i][0] = pos_orig[i][0];    positions[i][1] = pos_orig[i][1];    positions[i][2] = pos_orig[i][2];    types[i] = 1;  }
  num_atom_bravais = spg_refine_cell(lattice,                                     positions,                                     types,                                     num_atom,                                     symprec); num_atom_prim = spg_find_primitive(lattice, positions, types,num_atom_bravais, symprec);
  for (i = 0; i < 3; i++) {    printf("%f %f %f\n", lattice[i][0], lattice[i][1], lattice[i][2]);  }  for (i = 0; i < num_atom_prim; i++) {    printf("%f %f %f\n",  positions[i][0], positions[i][1], positions[i][2]);  }
SpglibDataset *dataset;const char *wl = "abcdefghijklmnopqrstuvwxyz";char symbol[11];spg_get_schoenflies(symbol, lattice, positions, types, num_atom, 1e-5);dataset = spg_get_dataset(lattice,                          positions,                          types,                          num_atom,                              1e-5);
printf("International: %s (%d)\n", dataset->international_symbol, dataset->spacegroup_number );printf("Hall symbol:   %s\n", dataset->hall_symbol );printf("Number o f symmetry operations: %d\n", dataset->n_operations);}######################################################################################Can someone tell me  what going wrong ? 
Thank you in advance ,Adlane