Carter Burwell chalks up his career to a series of fortunate accidents. Formally trained as a computer scientist, he studied animation and electronic music at Harvard, then wended his way to Cold Spring Harbor Laboratory, where he was the chief computer scientist for a few years. He has gone on — somewhat to his own surprise — to score more than 80 motion pictures, ranging from box-office biggies (“Twilight,” “Rob Roy,” “True Grit,” “Fargo”) to cult classics (“The Big Lebowski,” “Being John Malkovich,” “Gods and Monsters”) to darker works (“Howl,” “No Country For Old Men”).