The talks in the Austrian capital will focus on drafting the text of the comprehensive nuclear deal.
Deputy foreign ministers from Iran and the six world powers are present in the today negotiations.
Abbas Araqchi is to lead Iran's negotiating team. Majid Takht-e Ravanchi is also present in the Thursday talks.
The expert teams of the two sides will coincidently discuss the attachments to the draft deal.
Araqchi and Takht-e Ravanchi have held five rounds of talks with Ms Schmid on writing the text of comprehensive nuclear deal.
Meanwhile, two round of discussions were held between Iranian and American delegations led by Iran's Foreign Minister Mohammad Javad Zarif and the US Secretary of State John Kerry.
Iran-US talks were aimed to remove the political and technical obstacles.