LA Times Interview w/Catherine Hardwick clearing up Rob music confusion.

Talk about the love theme for the movie. There seems to be some confusion over Robert Pattinson’s role when it comes to that music ...

Maybe you can help me with that! People are very confused because they think that Rob wrote the love theme for the movie and that we chose not to use it and we used Carter Burwell, the composer, instead. That is actually not what happened. I’ve been wanting to tell someone this.
I asked Robert if he was interested in writing the love theme and he went, ‘Not really. No, that’s not my thing.’ I mean he’s not like an artist that you give an assignment to and he completes the assignment. For Rob, it flows out of him. He’s more of an organic artist. When he feels something that’s when he creates. You can’t tell him, ‘Do this. Do a love theme for Bella that will be used throughout the movie and translates to six different instruments.’ That’s not the way he creates. So, he never wrote a love theme for Bella.

What he did the day we shot the piano for the first time was he sat down and improvised for the hour we filmed. He improvised beautifully. I mean, he’s such a musician. Just beautiful things and melodies, but it wasn’t an intentional theme that could be used in different parts of the movie and developed and orchestrated with the violins and everything. He just let it flow. So the composer, Carter Burwell, did compose this beautiful love theme and that is developed in the early stages, in biology class, and then it keeps growing and goes through different instrumentations, and finally recorded with a full orchestra. When we re-shot the scene, Rob played that love theme on the piano.

About Rob handling the pressure in Rome:

I think it’s overwhelming for the cast. Kristen is very tiny and they get jostled around. I was a little bit scared for her. I think Rob likes it a little bit more than that. But imagine, every girl that walked up there to get there book signed, they would ask, ‘Can we kiss you?’ and the bodyguard would say no, and then they would just jump over the table and kiss him. Oh yes. ‘Can we take your photo?’ The body guard would say no, and they would just lean in and take it. It’s kind of funny, it’s kind of intense. But Rob has a great spirit. He makes it funny in a way. He’s wonderful.

Source LATimes.com