The Default Force Field

Covalent radii for all the elements are readily available and the bond orders of all bonds are available from the molecular graph. Prior to describing the explicit default parameter scheme, it is nec- 

An estimate of the hybridization state of an atom in a molecule can be obtained from the group of the periodic table that the atom resides in (which describes the number of valence electrons) and the connectivity (coordination of the atom). The HyperChem default scheme uses this estimate to assign a hybridization state to all atoms from the set (null, s, sp, sp, sp -, and sp ). The special 

The number of neighbors is given by the molecular graph and the following rules determine a hybridization state for each atom in a molecule. 

If the number of valence electrons is 0 or 8, the hybridization is described as null. This is used for Group 0 (Inert gases). 

If there are 3 neighbors and one or more of them is connected by an aromatic bond, then the hybridization is set to sp - or the hybridization is set to sp.  

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In Sections 17.11-17.14, we will manipulate the force field. Momec3 has a built-in standard force field that can be restored in the project-systems-system-forcejields section by using the defaults option. One can either modify the existing force field, and restore it to the default force field later or add an (empty) force field and set it to the Momec3 default by pressing default When you work on a copy of the force field, remember to select the correct force field when submitting jobs via calc-queue-add. 

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