In investor terms, the valuation of IP is the income it generates over time.
Without market traction, or some sort of patent protection, it is difficult to come up with a solid number. IP evaluation companies would be happy to do all the market research to determine the potential revenue that could be generated - but that conveniently leaves out the fact that market adoption isn't solely based on technical capabilities. Customer development is important as well.
There is a neat calculator that you can use to determine a running companies valuation - but a project does not a company make.
I'll assume that are looking for a defensible methodology to refer to, vs hiring a ip valuation services company - here is a good stanford university study entitled "what is your software worth?" that may be of interest to you.
You could conjure up a number you believe the software is worth, but an educated guess is still a guess. But - if that is the hurdle you must pass to get investor commitment, then so be it.