Q. I’m wondering about omitting the periods for US Department of Energy. On its site, it’s U.S. Do we follow the department’s preference or Chicago style?

A. The name of the organization is the United States Department of Energy. When you follow Chicago style to write “US Department of Energy,” you are abbreviating the fuller form of the name. The abbreviation at probably follows the GPO Style Manual, published by the US Government Publishing Office. GPO style uses periods in “U.S.” (and “U.K.” and the like), and those periods are a matter of government style. But unless you’re writing for the government, it is safe to omit them.