The study is entirely based on first principles simulations. So even though these may be the most accurate calculations we can possibly carry out... they still

The study is entirely based on first principles simulations. So even though these may be the most accurate calculations we can possibly carry out... they still may not be experimentally validated (for any number of reasons). In this case they cannot state anything as 100% truth as it has not (necessarily) been tested through experiment. "should" is appropriate.