user3872: As a person(~2170 uscf) who has recently started playing the scandinavian defense(Qd6), and has played against the scandinavian defense on the white side, I find it hard to get any sort of meaningful edge as white and often pretty much equalize with black. Yet in the top level, it's rarely seen in classical chess. Thus, it seems that there should be particular variations in the Qa5, Qd6, and Qd8 scandinavians that put it out of business. What are these lines?

user-1: There's nothing wrong with the Scandinavian. The reason why it has fallen out of favor is because it gives White a slight advantage, and Black loses some tempi with the queen.

user15478: Here are some lines. They seem to be the mainlines from the master database on Lichess. White is not winning, but the opening phase went White's way.
...Qd6
 [fen ""]
    1. e4 d5 2. exd5 Qxd5 3. Nc3 Qd6 4. d4 Nf6 5. Nf3 (5...a6 6. g3 Bg4 7. Bg2 Nc6 8. O-O O-O-O
    9. h3 Bh5 10. Bf4) c6 6. Ne5 Nbd7 7. Nc4 Qc7 8. Qf3 {note that this move prevents ...b5!!} Nb6 9. Bf4 Qd8 10. Be5 (10. h3 Qxd4?! 11. Rd1 Qc5 12. Be3 {is very good for White}) Bg4 {if not played now, White will prevent it with h3 and then O-O-O} 11. Qg3 {Black has to defend his g4-bishop now, as it is hanging after Bxf6}

...Qa5
[fen ""]
1. e4 d5 2. exd5 Qxd5 3. Nc3 Qa5 4. d4 Nf6 5. Nf3 c6 6. Bc4 Bf5 7. Bd2 e6 8. Nd5 Qd8 9. Nxf6+ gxf6 (9...Qxf6 10. Qe2 {with O-O-O next}) 10. O-O

...Qd8
[fen ""]
1. e4 d5 2. exd5 Qxd5 3. Nc3 Qd8 4. d4 Nf65. Nf3 Bg4 6. h3 Bxf3 (6...Bh5 7. g4 Bg6 8. Ne5 Nbd7 9. Nxg6 hxg6 10. g5 Nh5 11. d5 {with a huge clamp, Black has problems to make purposeful development}) 7. Qxf3 c6 8. Be3 e6 9. Bd3 Nbd7 10. O-O-O


3872: <p>As a person(~2170 uscf) who has recently started playing the scandinavian defense(Qd6), and has played against the scandinavian defense on the white side, I find it hard to get any sort of meaningful edge as white and often pretty much equalize with black. Yet in the top level, it's rarely seen in classical chess. Thus, it seems that there should be particular variations in the Qa5, Qd6, and Qd8 scandinavians that put it out of business. What are these lines?</p>
 -1: <p>There's nothing wrong with the Scandinavian. The reason why it has fallen out of favor is because it gives White a slight advantage, and Black loses some tempi with the queen.</p>
 15478: <p>Here are some lines. They seem to be the mainlines from the master database on Lichess. White is not winning, but the opening phase went White's way.</p>
<p>...Qd6</p>
<pre><code> [fen &quot;&quot;]
    1. e4 d5 2. exd5 Qxd5 3. Nc3 Qd6 4. d4 Nf6 5. Nf3 (5...a6 6. g3 Bg4 7. Bg2 Nc6 8. O-O O-O-O
    9. h3 Bh5 10. Bf4) c6 6. Ne5 Nbd7 7. Nc4 Qc7 8. Qf3 {note that this move prevents ...b5!!} Nb6 9. Bf4 Qd8 10. Be5 (10. h3 Qxd4?! 11. Rd1 Qc5 12. Be3 {is very good for White}) Bg4 {if not played now, White will prevent it with h3 and then O-O-O} 11. Qg3 {Black has to defend his g4-bishop now, as it is hanging after Bxf6}
</code></pre>
<p>...Qa5</p>
<pre><code>[fen &quot;&quot;]
1. e4 d5 2. exd5 Qxd5 3. Nc3 Qa5 4. d4 Nf6 5. Nf3 c6 6. Bc4 Bf5 7. Bd2 e6 8. Nd5 Qd8 9. Nxf6+ gxf6 (9...Qxf6 10. Qe2 {with O-O-O next}) 10. O-O
</code></pre>
<p>...Qd8</p>
<pre><code>[fen &quot;&quot;]
1. e4 d5 2. exd5 Qxd5 3. Nc3 Qd8 4. d4 Nf65. Nf3 Bg4 6. h3 Bxf3 (6...Bh5 7. g4 Bg6 8. Ne5 Nbd7 9. Nxg6 hxg6 10. g5 Nh5 11. d5 {with a huge clamp, Black has problems to make purposeful development}) 7. Qxf3 c6 8. Be3 e6 9. Bd3 Nbd7 10. O-O-O
</code></pre>
