Molecular Configurations over Energy

Recall that there are two types of molecular energy potential energy, such as that stored within a chemical bond, and kinetic energy, which includes translational, vibrational, and rotational motion. In this discussion we will not consider vibrational and 

In summary, as a system evolves to states with more possible configurations (spatially or energetically) of its molecular states (more probable), its entropy increases. 

SOLUTION A paramagnetic material consists of many unpaired electrons, each of which has a definite spin state (spin-up or spin-down). In the absence of a magnetic field, the energies of 

For every three molecules that react, only two molecules form this effect also contributes to the decrease in the spatial component of entropy. 

The entropy of this system can be thought of as having two components, that due to 

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Table 13-2. Vertical electronic n —> 7T transition energy of acetone in gas phase, Egas, and aqueous solution, Ewat, in units of eV. Excitation energy in aqueous solution was obtained from the combined QM/MM calculations treating acetone molecule at the quantum mechanical level of theory as indicated in the first column and using the polarizable potential for water molecules as a statistical average over 1200 molecular configurations extracted from classical MD simulation. The solvent shift in excitation energy, AE (in cm-1), is evaluated as a difference between excitation energies in water and in vacuum...

The Monte Carlo method, which is an alternative to molecular dynamics, consists of the generation of a sequence of molecular configurations in such a way that there is a Boltzmann distribution in the potential energies of the selected configurations. Then, the average of a molecular property over all configurations gives the appropriate value for comparisons with experiment. This method can only be u.sed to calculate equilibrium properties of a system, while equilibrium, transport (e.g., diffusion coefficients), time dependent (e.g., time correlation functions), and spectroscopic (e.g., infrared and Raman lineshapes) properties are accessible to calculation with the molecular dynamics method. 

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