Soft Power and Iran's Nuclear Diplomacy and world powers (Case Study: Joint Comprehensive Plan of Action)

Diplomacy between Islamic Republic and 5 group on Iran’s nuclear program which accomplished to “Joint Comprehensive Plan of Action” in July 2015, more than ever, is considering by public affairs and to challenge the attitudes.
Some issues are arising from this event, and the main question is what causes the success and fruition of Iran's nuclear talks with the world powers after 12 year talks?
Most of the writers and analyzers around the world, by reviewing the atmosphere of Iran and the United States diplomacy, claim these governments were seeking the model of soft power to reach the agreement on Iran’s nuclear program. The main question in this topic is how the soft power could lead the negotiations to Iran nuclear deal?
The authors of this essay believe, despite the differences in objectives of Iran and US, two countries could reach the deal and settle it just by using peaceful means such as negotiation, interaction, changing the tone and rhetoric, persuasion and multilateralism.