Hi, I am quite confused with few concepts and relations between quantum mechanics and statistical physics. Here it goes: 1. In quantum mechanics, we can calculate the energy levels of a bound state (confining potential). So in short, we calculate all possible energy level that a system could have in any state of this given system. 2. In room temperature, statistics of particles can be approximated by Boltzmann statistics. And physical quantities can be calculated using partition function. 3. As temperature goes down, there will be distinction between fermions and bosons, where Fermi-Dirac and Bose-Einstein statistics must be used respectively, instead of Boltzmann statistics. Then, again, with partition function, we can calculate physical quantities that we are interested with. So .. my question is, is there any connection between calculated energy from quantum mechanics with the partition function? Is the energy levels calculated with quantum mechanics will be like that forever in any condition? How about the relation with the change of temperature? I feel like my understanding is in mess right now. The more book I read, the more confused I am .. Thanks in advance!