If Catherine Ashton and Mohammad Zarif do indeed meet, it is very unlikely that anything will come of the meeting. There have been many attempts at diplomatic solutions to the issue of Iran’s nuclear program and none of those attempts have done much good. While Zarif is new in office, as is President Rouhani, there is no reason to believe that Iran’s position on its nuclear program has changed.
Iran’s position on its nuclear program appears to be fixed. At the highest levels, the country sees a nuclear program as its right. It does not believe that it should have to have permission from anyone to have what it insists is a peaceful program. At the same time, the EU’s position does not appear to have much wiggle room either. In addition, the EU does not appear to have any real leverage over Iran. There is no way that Russia or China will allow any serious UN action against Iran.
What this means is that Iran and the EU have fixed positions on this issue and neither has much leverage over the other to make the other change. Therefore, it is very unlikely that anything concrete will come from this meeting.