MD simulations can help [to] gain molecular-level insights into the behavior of solutes in a specific biphasic system.
I'm not sure if it is "help gain" or "help to gain", or maybe "help gaining"; the second sounds more natural to me. I know we can say "help me find/gain/etc." but saying "help find/gain/etc." sounds odd to me. Could you please say what is the rule for these cases (with and without an object)