Energy landscape properties studied by symbolic sequences
  We investigate a classical lattice system with $N$ particles. The potential energy $V$ of the scalar displacements is chosen as a $\phi ^4$ on-site potential plus interactions. Its stationary points are solutions of a coupled set of nonlinear equations. Starting with Aubry's anti-continuum limit it is easy to establish a one-to-one correspondence between the stationary points of $V$ and symbolic sequences $\bm{\sigma} = (\sigma_1,...,\sigma_N)$ with $\sigma_n=+,0,-$. We prove that this correspondence remains valid for interactions with a coupling constant $\epsilon$ below a critical value $\epsilon_c$ and that it allows the use of a ''thermodynamic'' formalism to calculate statistical properties of the so-called ``energy landscape'' of $V$. This offers an explanation why topological quantities of $V$ may become singular, like in phase transitions. Particularly, we find the saddle index distribution is maximum at a saddle index $n_s^{max}=1/3$ for all $\epsilon < \epsilon_c$. Furthermore there exists an interval ($v^*,v_{max}$) in which the saddle index $n_s$ as function of average energy $\bar{v}$ is analytical in $\bar{v}$ and it vanishes at $v^*$, above the ground state energy $v_{gs}$, whereas the average saddle index $\bar{n}_s$ as function of energy $v$ is highly nontrivial. It can exhibit a singularity at a critical energy $v_c$ and it vanishes at $v_{gs}$, only. Close to $v_{gs}, \bar{n}_s(v)$ exhibits power law behavior which even holds for noninteracting particles. 
Rolf Schilling