I think both Marcel's(noisy) and Melrose(very quiet) are open Sunday. Both have excellent food. I have not been to Viadalia since it reopened.

Seasons, & Citonellel are also both open on Sun.

Due to the tourist influx, very few places in DC expect coat and tie. I wear a sport coat into most places to keep warm, and usually look out of place.

edited to add: Tosca if you wish to do Italian. Very quiet, very elegant, the class Italian restaurant of DC and is open on Sun.

I am not a fan of Kinkead, Galileo, Taberna or Nora. I do not know if they are open or closed on Sun.