C2A (Coarse to Atomic) package will take you as far as adding full atomic detail to a coarse-grain template, but you will still need to minimize the full atomic structure using a physics-based MD engine.
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Jonikas MA, Radmer RJ, Altman RB.
Knowledge-based instantiation of full atomic detail into coarse-grain RNA 3D structural models.
Bioinformatics. 2009 (2009)