Time evolution of natural orbitals in ab initio molecular dynamics

This work combines for the first time ab initio molecular dynamics (AIMD) within the Born-Oppenheimer approximation, with a global natural orbital functional (GNOF), an approximate functional of the one-particle reduced density matrix. The most prominent feature of GNOF-AIMD is the ability to display the real-time evolution of natural orbitals, providing detailed information on the time-dependent electronic structure of complex systems and processes, including reactive collisions. The quartet ground-state reaction N($^4$S) + H$_2$($^1\Sigma$) $\rightarrow$ NH($^3\Sigma$) + H($^2$S) is taken as validation test. Collision energy influences on integral cross sections for different initial ro-vibrational states of H$_2$ and rotational-state distributions of NH product are discussed, showing a good agreement with previous high-quality theoretical results.