At classical harmonic oscillator, total energy is proportional to square of frequency, but at quantum harmonic oscillator, total energy is proportional to frequency. Are those two frequencies the same? How it is with transition from quantum harmonic oscillator to classical harmonic oscillator? How omega^1 and omega^2 agree? One example of this is http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/hosc6.html but where is the frequency? Maybe I found answer: http://en.wikipedia.org/wiki/Correspondence_principle Is this enough?