EEG frequency bands depend on species, brain area, and task, and categorizing them is more of an art than a science.  If you are looking at rodent LFP, then we can say that theta is 6-12 Hz.  If it is human LFP, then theta is 4-7 Hz.  Defining delta as 0.5-4 Hz seems fine either way.

Thank you very much! Are there any good references that give a general overview of this topic? I work primarily with mice. Thanks again!

buzsaki 2002 is the well cited paper, but look at more recent work from their lab as well. i particularly like schomburg 2014 because it discusses where the lfp comes from

I'll have a look. Thanks again!