(Meta-)stable structures of an atomic system corresponds to minima on the potential energy surface (PES) of the system. The PES has the number of dimension that equals to the degrees of freedom of the system. With increasing the degrees of freedom of the system, computational costs of electronic structure calculation and also the numbers of minima on the PES increase so that the efficient method is required for the structural prediction.
Anharmonicity of the PES gives us a hint in what direction its minima are located [1,2]. When we escape from a minimum and approach saddles, the PES is distorted from the harmonic PES that considered at the minimum because of the difference of the signs of curvature between minima and saddles. We develop a structural prediction method utilizing this marked characteristic of the PES. In our method, we consider the imaginary PES V(x), which is a sum of the original PES U(x) and an additional term filling a known minimum. We construct the filling term so that it rapidly decays as x depart from the harmonic region. Then, V(x), the minimum is raised above the neighboring saddle points and therefore the neighboring minima can be found by structural relaxation based on V(x).
[1] K. Ohno and S. Maeda, Chem. Phys. Lett. 384, 277 (2004).
[2] S. Maeda and K. Ohno, J. Phys. Chem. A 109, 5742 (2005).