user4271: If few best computer players would be playing against themselves, chances of white winning would depend on the opening used. That way after simulating thousands of games the best opening would be found that is strictly better than the others. 
Is there a flaw in this procedure? Has this ever been done before?

user924: Such a process would only find out which opening works best against the current version of itself. Nobody cares how well a computer plays against itself.
For some computer vs computer events (like TCEC), it is common practice to pick some opening position after 8 moves or so, and then play without opening book.
For customers, people who buy engines to play games against it, it is most important that it plays a wide variety of openings (variety is more fun), and that it is very up to date with current theory, for practice reasons.
So the main people interested in really great opening books for computer vs computer play are the kind of people who run their engines 24/7 on sites like Playchess to play against other computers, trying to improve their computers' ratings. They basically do this process manually, by watching the results and updating the opening books by hand where needed.
And on top of all that, remember that chess is most likely a draw. All the very theoretical, forced, deep lines that computers are great at analyzing out (like the Najdorf Poisoned Pawn, say) tend to lead to forced draws in all lines. Once everybody knows too much, they have to switch to something less well known.

user3819: You may underestimate the number of games you need to determine the "best" opening by simulation. The differences between different openings are very small and to get a solid statistical judgment a few thousand games for each opening may be insufficient.
Then comes the question of the best response: There is an opponent, after all, and to build an opening book you must test for the strongest responses.
Still, this is all statistical and we know that it is not possible to solve chess computationally at the time being. A deep analysis may find a flaw in the "best" opening that is out of sight for current chess engines.
To your last question: For the chess variant "Schoolbook" (a variant of the Carrera-Capablanca type with rook-knight and bishop-knight compounds) its author Sam Trenholme has started to build an opening book using the method you propose, see http://www.chessvariants.org/index/msdisplay.php?itemid=MSschoolbook (comment at the bottom of the page).

4271: <p>If few best computer players would be playing against themselves, chances of white winning would depend on the opening used. That way after simulating thousands of games the best opening would be found that is strictly better than the others. 
Is there a flaw in this procedure? Has this ever been done before?</p>
 924: <p>Such a process would only find out which opening works best against the current version of itself. Nobody cares how well a computer plays against itself.</p>

<p>For some computer vs computer events (like TCEC), it is common practice to pick some opening position after 8 moves or so, and then play without opening book.</p>

<p>For <em>customers</em>, people who buy engines to play games against it, it is most important that it plays a wide variety of openings (variety is more fun), and that it is very up to date with current theory, for practice reasons.</p>

<p>So the main people interested in really great opening books for computer vs computer play are the kind of people who run their engines 24/7 on sites like Playchess to play against other computers, trying to improve their computers' ratings. They basically do this process manually, by watching the results and updating the opening books by hand where needed.</p>

<p>And on top of all that, remember that chess is most likely a draw. All the very theoretical, forced, deep lines that computers are great at analyzing out (like the Najdorf Poisoned Pawn, say) tend to lead to forced draws in all lines. Once everybody knows too much, they have to switch to something less well known.</p>
 3819: <p>You may underestimate the number of games you need to determine the "best" opening by simulation. The differences between different openings are very small and to get a solid statistical judgment a few thousand games for each opening may be insufficient.</p>

<p>Then comes the question of the best response: There is an opponent, after all, and to build an opening book you must test for the strongest responses.</p>

<p>Still, this is all statistical and we know that it is not possible to solve chess computationally at the time being. A deep analysis may find a flaw in the "best" opening that is out of sight for current chess engines.</p>

<p>To your last question: For the chess variant "Schoolbook" (a variant of the Carrera-Capablanca type with rook-knight and bishop-knight compounds) its author Sam Trenholme has started to build an opening book using the method you propose, see <a href="http://www.chessvariants.org/index/msdisplay.php?itemid=MSschoolbook" rel="nofollow">http://www.chessvariants.org/index/msdisplay.php?itemid=MSschoolbook</a> (comment at the bottom of the page).</p>
