Tunneling ionization of the F4 and D6 states of vanadium: Exchange blockade

Abstract

Using TDDFT calculations we compare tunneling ionization of the a 4 F ground state and the a 6 D first excited state of vanadium in laser fields of intensities between 1.4 and 4.0×10 13 W/cm 2 .The calculated ionization yields of the ground state of vanadium were already shown to agree well with experimental results [Chu and Groenenboom, Phys. Rev. A 94, 053417 (2016)]. We find that the tunneling ionization rate of the sextet state is lower than that of the quartet state. This is surprising, since the ionization potential of the sextet is lower than that of the quartet state.This finding, however, is consistent with the experimental observation that niobium, whose ground state is a 6 D 1/2 , has a much smaller ionization yield than vanadium (a 4 F 3/2 ), even though their ionization potentials are extremely close [Smits et al., Phys. Rev. Lett. 93, 213003 (2004)]. Our calculations demonstrate the existence of exchange blockade for the higher spin state. It arises from a strong field dynamic effect that the highest and second highest electrons mixing in the same set of unoccupied spin orbitals, which causes an isotropic attractive potential that confines the electrons close to the core.

Suppressed and enhanced tunneling ionization of transition-metal atoms and cations: A time-dependent density-functional-theory study on nickel

“…Another TDDFT study demonstrated the difference that the electronic structure can make in TI by comparing the ground state of vanadium [(3d 3 4s 2 ) 4 F ] to the (3d 4 4s) 6 D excited state. Even though the ionization potential of the 4 F quartet state is higher than that of the 6 D sextet state, the TI rates of the sextet turned out to be lower because of exchange blockade for the higher spin state [17].…”

“…We adopt an all-electron TDDFT method for treating openshell atoms. This approach was implemented for the neutralatom vanadium and explained its suppressed TI [15,17]. It is an optimized effective potential (OEP) formalism, which correctly accounts for the long-range exchange-correlation potential.…”

Many-electron dynamics in high-order harmonic generation of niobium: A time-dependent density-functional-theory study

“…A TDDFT method with an optimized effective potential formalism was developed for studying the tunneling ionization of vanadium [19,25] and nickel [26]. In the TDDFT analysis, the ionization suppression of the neutral atoms and the enhancement of the cations were explained in terms of the AC Stark shifts, elevated tunneling barrier, exchange blockade, and the large centrifugal barrier for the d orbitals [26].…”