Welcome to the NITROGEN website!

Note: version 1.10 is the final release of NITROGEN 1.x. A permanent link is hosted by Zenodo. Further development is being carried out with NITROGEN 2, a Python package.

NITROGEN (Numerical and Iterative Techniques for Rovibronic Energies with General Internal Coordinates) is a program for calculating variational and perturbative rovibrational and rovibronic energies and wavefunctions of small to medium sized molecules. The combination of discrete variable representation (DVR) bases and numerical kinetic energy operator (KEO) evaluation enables the program to support general curvilinear internal coordinate systems. By taking advantage of sparse iterative linear algebra techniques, large rovibrational Hamiltonian matrices can be efficiently diagonalized. NITROGEN was developed with flexibility in mind. Via user-programmed external libraries, custom coordinate systems and Hamiltonians can be interfaced with the main program, making NITROGEN suitable for treating a large variety of molecules. Implementations of curvilinear coordinate VSCF, VMP2, and VCI are also available. Extensions of VMP2 provide effective quartic rotational and rovibrational Hamiltonians.

NITROGEN is a research code written by Bryan Changala (graduate student at JILA/CU-Boulder Dept. of Physics).