Elo change of engine from pure material to very good evaluation

Question

I am currently rewriting a chess engine with a friend. We decided to first work on the search and only later if the search works really well, we will do some very good evaluation.

The engine itself evaluates the board with pure material evaluation + piece square tables. We hit around 6Mnps and it competes with 2000 CCRL engines right now.

I was wondering how much ELO-Gain could we expect if we replace the evaluation at some point with another evaluation. Or more like: How much ELO can an evaluation function give?

I mean obviously, if you would replace the evaluation of stockfish with nothing but 0, it would do random moves and lose over 3000 ELO points but I am talking about the ELO difference between a very basic evaluation function and an insanely good evaluation function which takes mobility, king safety, pawn structure, game phase, etc. into account.

Answer 1

The currently best eval function is a leela net. At a single node, some leela nets are in the 2500 elo range. The drawback of course is that they are about 1000x slower than a SF eval (assuming a somewhat modern gpu, cpu). SF eval is obviously way weaker than this, but it wouldn't surprise me if is 500 elo stronger than a simple eval function.

Answer 2

The difference is huge, worth well over a thousand elo. See SimpleEval, which is Stockfish with a very simplified evaluation function. It's not strong enough to beat top humans, even though Stockfish itself of course is, by a huge margin.

The reason for this is that search doesn't work well without a strong evaluation function. You are less able to tell which branches you should prune.