Anharmonic oscillator model of the free volume theory for liquids

The anharmonic oscillator model of the free volume theory for liquids is de rived quite strictly using the method of summing over the lattice sites. Th e normal boiling point calculated is notably improved as compared with that in the LID theory. It is shown that the equal probability average of the L JD theory would lead to large errors in evaluating some physical quantities . The method is convenient to be extended to more universal potential funct ions and to consider the quantum effects of low temperature liquids.