where nk is the number of quanta deposited in vibrational mode k, and  denotes a particular ensemble   k n . Thus, to know the number of microstates, we must determine the number of solutions of Eq. ( ). This means the number of ways we can distribute different values of nk among the vibrational modes, keeping E constant. Despite the simplicity of this formulation, it is a formidably tricky problem to solve analytically. We can approach it numerically, but the number of microstates is so large that it may become unattainable to compute even for a molecule with only six atoms.