particle_list = [
            (1,  1, espressopp.Real3D(5.5, 5.0, 5.0), 1.0, 0),
            (2,  1, espressopp.Real3D(6.5, 5.0, 5.0), 1.0, 0),
            (3,  1, espressopp.Real3D(7.5, 5.0, 5.0), 1.0, 0),
            (4,  1, espressopp.Real3D(8.5, 5.0, 5.0), 1.0, 0),