Questioning the I-V characteristics of DTB device

[mephisto3142001]

I compared the result of I-V characteristic of DTB device in tutorial "ATK Tutorial for Molecular Devices"  with the I-V  characteristic published in "Comp. Mat. Sci. 27, 151 (2003) ". The result shows slight difference at the region (1.6V ~ 3.0V and -1.6V ~ -3.0V).          The I-V curve is ohmic with smaller slope in  in tutorial "ATK Tutorial for Molecular Devices". However, the I-V is almost horizontal in "Comp. Mat. Sci. 27, 151 (2003) ". The parameters setting is followed  by both the tutorial and the paper. I deemed that the same calculation method (no matter what package, like TranSiesta or Virtual NanoLab is used) should result in the identical I-V characteristic, so I wonder which one is more correct or which fact may cause such the difference.

[kstokbro]

The original paper only used one k-point in the transverse direction, since the version used at that time did not include the k-point sampling in the transverse directions.
Since then we have learned that using a single k-point  is not sufficient for a gold electrode, and the tutorial is done with 3x3 k-points which is OK. Thus, the result in the tutorial is more trustworthy than the paper, however, i find that the results are not radically different.
Besides this, the geometry, pseudo potentials and basis sets are not identical in the two calculations, however, this should be of minor importance.