I am new to MS.I have build my cell (Pure Ni) and then have build nano cluster with substitution of Ga. Then I am trying to do geometry optimisation. Compass is not working. Unable to assign Ga. But using universal forcefield I am able to assign Ni and Ga and calculate. But I am not sure about how to choose algorithm. How do I know which algorithm will give best convergence? My next step isto run mechanical property. I want to get Elastic mosulus.