The 23-year-old Thompson was the Florida Marlins first-round selection (22nd player chosen overall) in the 2005 First-Year Player Draft. After four full seasons of action in the Florida farm system, Thompson was acquired by Washington in a deal for first baseman Nick Johnson on July 31, 2009.
Thompson spent a majority of the 2010 season with Double-A Harrisburg, where he made 26 starts and pitched 136.2 innings. He also posted a victory in one start with Triple-A Syracuse on April 24.
Atkins, 31, was signed as a free agent last December by Baltimore and hit .214 with a homer and nine RBI in 44 games last season before being released by the Orioles on July 6.
An eight-year Major League veteran, Atkins made his debut with Colorado in 2003 and played with the Rockies thru the 2009 season before becoming a free agent. In his big league career, Atkins has made 632 appearances at third base, 105 at first base and six in the outfield.