Gray Code Optimization (GCO) algorithm is a deterministic algorithm based on the Gray code representation. It sometimes suffers from slow convergence and sub-optimal solutions. Expectation Maximization (EM) algorithm is used to analyze how the GCO explores the search space. The results indicate that it is similar to generating samples with a mixture Gaussian distribution. Based on these findings, a novel stochastic optimization algorithm based on the mixture Gaussian model is proposed. The new algorithm is applied to molecule conformation search. Obtaining global minimum energy conformations of molecule is a very hard optimization problem. The difficulty arises from the following two...