One book you should also read if you are interested in either analyzing or composing atonal music is The Structure of Atonal Music by Allen Forte. It explains the basic concepts, vocabulary, and language that analysts and composers of atonal music use. Pitch class sets, interval vectors, relations and set complexes. As an atonal composer, pitch class set theory has been extremely helpful in composition. The interval vectors not only show you what intervals occur in the pitch class set, but also the ones that do not occur and are not available. That helps you in designing the specific sound and character you want to achieve.