Both are developed at the University of Groningen, and at the Computer-Aided Chemistry Group[1] at the Laboratory for Physical Chemistry[2] at the Swiss Federal Institute of Technology (ETH Zurich).
[3] The united atom force field was optimized with respect to the condensed phase properties of alkanes.
The van der Waals force parameters were derived from calculations of the crystal structures of hydrocarbons, and on amino acids using short (0.8 nm) nonbonded cutoff radii.
[5][6] The force field was also improved, e.g., in the following way: aliphatic CHn groups were represented as united atoms with van der Waals interactions reparametrized on the basis of a series of molecular dynamics simulations of model liquid alkanes using long (1.4 nm) nonbonded cutoff radii.
The A-version applies to aqueous or apolar solutions of proteins, nucleotides, and sugars.