Molecular vibrations zero point energy

In reality, even if a molecular species is at absolute zero, it will contain vibrational zero-point energy quantum mechanically. How to build this into a classical trajectory calculation is one of the enduring problems in this field. 

The thermochemistry section of the output also gives the zero-point energy for this system. The zero-point energy is a correction to the electronic energy of the molecule to account for the effects of molecular vibrations which persist even at 0 K. 

In order to predict the energy of a system at some higher temperature, a thermal energy correction must be added to the total energy, which includes the effects of molecular translation, rotation and vibration at the specified temperature and pressure. Note that the thermal energy includes the zero-point energy automatically do not add both of them to an energy value. 

Zero Point Energy. The energy of molecular vibration at OK. 

Zero Point Energy. The energy of molecular vibration at OK, given as half the sum of the Vibrational F requencies times Planck s constant. 

From a theoretical perspective, isotope effects are fairly trivially computed. The stationary points on the PES and their electronic energies are independent of atomic mass, as are the molecular force constants. Thus, one simply needs to compute the isotopically dependent zero-point energies and translational, rotational, and vibrational partition functions, and evaluate Eq. (15.33). 

One way to distinguish between the two possibilities is to study the isotope effect on the kinetics of vinyl acetate polymerization and on the polymer molecular weight. The deuterium isotope eftect has been ascribed to the difference in the zero point energies of the stretching vibrations of the C-H and C-D bond (11). The rate of a reaction in which deuterium is transferred is slower than that of the corresponding reaction for hydrogen, since the C-D bond has a lower zero point energy. 

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