It is the BGM from Steins;Gate 0 Episode 16 "無限遠点のアルタイル -Vega and Altair-", 19:35. 楽譜→ https://www.douban.com/note/599300855/My Youtube Channel→ https://www.youtube.com/channel/UCddtyyzHy8J3uTEgsiIgKgQ
http://www.nicovideo.jp/watch/sm33870298