The DNA parameter files have had very limited usage. Do not trust the results using them unless you satisfy yourself that the parameters are reasonable.
The DNA parameters are inconsistent with the protein parameters. Do not mix proteins and DNA together. You will run into problems with chemical type codes being reused and general confusion and errors.
PARMDNA4 is the same as PARMDNA3 except a sodium ion has been added to the nonbonded parameters.
* PARAMETER FILE -- VERSION 4 -- CREATION RUN -- 10/20/81 -- BRB
Title in the file:
* PARAMETER VERSION 4 * DNA