Temperature controls the probability of accepting a higher-energy candidate during the search. At higher temperatures, the method can tolerate more energy-increasing moves, which promotes exploration of alternative molecular states. As cooling proceeds, those moves become less likely, so the search increasingly favors lower-energy arrangements and spends more effort refining promising regions.
A strictly downhill search may become trapped after reaching a locally favorable state, even when a better solution lies elsewhere. Simulated annealing can temporarily accept higher-energy states, allowing the search to cross unfavorable regions and leave that trap. This exploratory behavior is useful when molecular conformations or model parameters create many competing energy minima.
The candidate being optimized must be expressed as a state, such as a molecular structure, conformation, or parameter set, and each state must have an associated energy. These two choices determine what the search can change and how it judges improvement. A meaningful representation and energy measure therefore connect the optimization process to the chemical problem being studied.
Gradual cooling preserves exploration early in the search, when accepting some higher-energy states can help locate different regions of the solution space. Reducing that acceptance too quickly would favor refinement before the method has adequately explored alternatives. Continued cooling then shifts the balance toward lower-energy states, supporting a more useful near-optimal result.
First, represent the molecular structure, conformation, or chemical-model parameters as a candidate state and assign it an energy. Generate successive candidate states, usually retaining lower-energy ones while sometimes accepting higher-energy alternatives. Finally, reduce the temperature progressively so acceptance of higher-energy states declines. The resulting state is treated as a useful approximate solution.
It is useful when a molecule may adopt many candidate conformations and exhaustive enumeration would be impractical. The method can explore alternative arrangements, occasionally move toward higher-energy conformations, and later emphasize lower-energy states as cooling progresses. This makes it suitable for identifying promising conformations without requiring every possible structure to be evaluated.
In reaction pathway studies, candidate states can represent alternative structures or pathway-related arrangements whose energies guide the search. For fitting complex chemical models, the states can instead represent parameter sets, with energy indicating how well each set performs according to the model's objective. In both cases, stochastic exploration helps address difficult search spaces where exhaustive testing is impractical.