Exploring Excited-State Potential Energy Surfaces: Nonadiabatic Couplings and Minimum-Energy Crossing Points

  • Nonadiabatic coupling (NAC) is the most important physical quantity governing transitions between electronic states, such as internal conversion and radiationless relaxation.

  • The minimum-energy crossing points (MECPs) in the seam space where multiple electronic states are degenerate are the most important points which connect photochemical reaction pathways.

  • NACs can be computed with standard CIS and TDDFT methods, as well as with the spin-flip (SF) CIS and TDDFT variants, which afford correct topology around conical intersections.

  • NACs can also be computed with EOM-EE/IP/EA-CCSD methods.

  • Multiple algorithms for MECP location are available, including those that do not require NACs.

Calculated NAC vectors for naphthalene

Calculated z-component of the derivative coupling between the 3\(^1\Sigma_g^+\) and 5\(^1\Sigma_g^+\) states of He\(_2\)