You can use the DATEPART to get just given parts of the DT filed.
Register Hereor login if you are already a member
Try using DATETIME2(0) and you'll see some space savings as well. From here I would start experimenting. If performance is poor just querying off the single column, I'd then try adding persisted computed columns to separate out the date and time components. This will ensure that the separated DATE and TIME columns will always be the same as the "master" DATETIME2(n) column.