A visual Fortran 90 program for the two-particle or two-hole excitations of nuclei: The PPRPA program

Random Phase Approximation (RPA) is one of the main approximation tools in studying nuclear structure. Here, we present a graphical user interface (GUI) Fortran code: Particle-Particle Random Phase Approximation (PPRPA) version 1, 2015. The code performs Tamm-Dancoff approximation (TDA) and Random Phase Approximation (RPA) calculations of nuclear structure of nuclei having A±2 nucleons in the total angular momenta and isospin (JT) scheme. The Hamiltonian is diagonalized with a given input model space, single-particle energies and interaction. Space function has been expanded to include orbits s, p, d, f, g and h. The current version of the code allows the user to test 20 orbits only. All possible eigenvalues and amplitudes within a model space are calculated. The single-particle density, charge distribution density and transition density are calculated in the basis of the harmonic oscillator potential. The primary utility of the PPRPA code is providing a visual tool to implementation and understanding of the collective excitation techniques TDA and RPA. Impact of the program includes all students, researchers and all those interested in knowing the facts about the structure of the atom nucleus and about the success of approximation methods in different branches of science.