Ring-polymer instanton theory for tunneling between asymmetric wells

Instanton theory has arisen as a practical tool for calculating tunneling splittings in molecular systems. Unfortunately, the original formulation of instanton theory fundamentally breaks down when trying to calculate the level splitting in asymmetric double wells, as there is no imaginary-time periodic orbit connecting the two non-degenerate minima. We have, therefore, developed a new formulation of instanton theory based on a projected flux correlation function that is applicable to these asym