New UNRES force field package with Fortan 90

UNRES is a coarse-grained model of polypeptide chains. Until now, each version of UNRES (UNRESPACK v.3.2 and earlier ones) has been written in Fortran 77. Due to the fact that Fortran 77 enables us to use only static arrays, the Fortran 77 version has significant memory problems, and consequently, UNRESPACK has had to be split into many programs. Our recent work was focused on creating a new UNRES package with Fortran 90 (UNRESPACK v.4.0), based on the previous Fortran 77 versions. Fortran 90 provides dynamic memory allocation, user defined data types, and structuring the code into modules which encompass subroutines, functions, and variables. Moreover, Fortran 90 adds internal functions and subroutines, providing greater flexibility. The whole code of UNRES with Fortran 90 has been restructured, so that it now consists of modules that can be assembled to create the main simulation program and companion programs. This approach enabled us to eliminate the redundancy of the code, while keeping all functions of the package.