Difference in experimental and MD simulation results

I am working on nanoindentation studies and as preliminary step nanoindentation of Nickel using rigid indenter. The hardness values obtained in the case of experimental studies are 4 GPa - 7 GPa, while MD simulation results are in the range of 20GPa, that is almost 3 to 4 times the experimental values.

  1. Why is such a huge difference in the computed values for MD simulations.

  2. Is there any proper literature to refer that give an in-depth idea about the difference in computed values.

It is hard to say exactly without seeing your simulation set up. If you would like to provide a summary of what you have done, a description of your simulation cell, and provide a concise input file with the important commands you can receive much better help from the mailing list.