The surface of the molecule is constructed in the following way. The Gaussian function is assigned to each atomic center:

where the r_a vector defines the position of atom a and R_a is a specific radius of atom a (as given in the pqr file). This Gaussian function has the following properties:

– at the nucleus center a its value is 2,

– at |r_a – r| = R_a it equals to 1 (i.e. half of its maximum value).

The volume occupied by a molecule (or molecular density) is defined as a sum over all atoms, a:

The surface of the molecule is defined as the surface corresponding to the isovalue of 1. The figures shown below present the van der Waals surface of a molecule (left) and its molecular surface computed using atom-centered Gaussian functions (right).

The definition of the surface of the molecule used by Surface Diver can be modified with the [irad] parameter.