The rest of the cast including Taylor Lautner, Peter Facinelli and Dakota Fanning are also not expected at the premiere of Breaking Dawn - Part 2 during the festival from November 9 to 17, which has been announced as the highlight of the Alice In The City sidebar, according to The Hollywood Reporter.
It comes as sources report to People that R-Patz and Kristen, who broke up in July after she admitted to having a fling with her Snow White And The Huntsman director Rupert Sanders, are a couple again.
They are scheduled to make their first red carpet appearance since the split as they do the press rounds for The Twilight Saga: Breaking Dawn - Part 2, which will be released in the UK on November 16.
Alice In The City focuses on films for a youth audience, although most of the films - with the exception of Breaking Dawn - will screen independently of the film festival.
The animated comedy Wreck-It Ralph, featuring the voices of John C Reilly, Sarah Silverman and Jack McBrayer, and DreamWorks' Rise Of The Guardians with the voices of Chris Pine, Jude Law and Hugh Jackman will also premiere, with the rest of the line-up yet to be announced.
The Rome International Film Festival will celebrate the career of French author and illustrator Jean-Thomas 'Tomi' Ungerer with a screening of Moon Man and a documentary.
American filmmaker Walter Hill, whose new film Bullet To The Head will premiere at the festival, will receive the Maverick Director award.