Nuclear repulsion energies

The iotal energy of a system is equal to the sum of the electronic energy and the Coulombic nuclear repulsion energy ... 

The potential energy of vibration is a function of the coordinates, xj,. .., z hence it is a function of the mass-weighted coordinates, qj,. .., q3N. For a molecule, the vibrational potential energy, U, is given by the sum of the electronic energy and the nuclear repulsion energy ... 

That is, the sum of the electronic energy and nuclear repulsion energy of the molecule at the specified nuclear configuration. This quantity is commonly referred to as the total energy. However, more complete and accurate energy predictions require a thermal or zero-point energy correction (see Chapter 4, p. 68). 

Finally, we should establish some index of steric repulsion since in certain instances it may not be immediately obvious which of two isomers is more destabilized by steric effects. The most convenient index is the nuclear repulsion energy, En, which can be calculated readily for any molecular system0. ... 

This order of stability is reflected in the nuclear repulsion energy, which constitutes an index of steric effects , as shown below ... 

Envc is the nuclear repulsion energy, and Rj here denote the coordinates of the i-th electron and -th nucleus, respectively. 

This does not mean that the energy of this T is independent of the actual angle in the molecule. Among other things, the nuclear repulsion energy depends upon the distance between the H atoms. 

The last set of terms is independent of the electrons and depends only on the coordinates of the nuclei. At a particular geometry, the sum of these terms provides the total nuclear repulsion energy, which is just an additive constant to the electronic energy. Consequently, the terms for the nuclear-nuclear repulsion energy in H can be neglected when attempting to solve Eq. 1 for the electronic wave functions and their associated energies. 

To complete the energy evaluation by the MNDO method, the nuclear repulsion energy is added to the SCF energy. The MNDO nuclear repulsion energy is computed as... 

A second modification recently described by Repasky, Chandrasekhar, and Jorgensen (2002) focuses on improving the core-repulsion functions in MNDO and PM3. In particular, they define a pairwise distance directed Gaussian function (PDDG) to compute a contribution to the nuclear repulsion energy between atoms A and B as... 

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