Modeling of Manganese Atom and Dimer Isolated in Solid Rare Gases: Structure, Stability, and Effect on Spin Coupling

Abstract

Structures and energies of the trapping sites of manganese atom and dimer in solid Ar, Kr, and Xe are investigated within the classical model, which balances local distortion and long-range crystal order of the host and provides a means to estimate the relative site stabilities. The model is implemented with the additive pairwise potential field based on the ab initio and best empirical interatomic potential functions. In agreement with experiment, Mn single substitution (SS) and tetrahedral vacancy (TV) occupation are identified as stable for Ar and Kr, whereas the SS site is only found for Xe. Stable trapping sites of the weakly bound Mn dimer are shown to be the mergers of SS and/or TV atomic sites. For Ar, (SS + SS) and (TV + TV) sites are close in energy, whereas (SS + TV) site lies higher. The (SS + SS) accommodation is identified as the only stable site in Kr and Xe at low energies. The results are compared with the resonance Raman, electron spin resonance, and absorption spectroscopy data. Reproducing the numbers of stable sites, the calculations tend to underestimate the matrix effect on the dimer vibrational frequency and spin-spin coupling constant. Nonetheless, the level of agreement is found to be informative for tentative assignments of the complex features seen in Mn matrix isolation spectroscopy.

Computational study of the stable atomic trapping sites in Ar lattice

“…Thus, Ar atoms of the movable set can adapt themselves to the force induced by embedded atom G, while the atoms of fixed set maintain the long-range periodic order of the host crystal. In contrast to our previous applications [10,19], where the sizes of the sets were chosen once by convergency of the results, we need here more flexibility to handle the variation of the guest-host interaction potential automatically. So the present model allows for slight tuning at each potential parameter choice, as described in the Sec.…”

“…The former was studied in Ref. 19 with the ab initio Mn-Ar potential function giving = 4.52 ρ Å and = 76 ε cm -1 . Using these parameters for LJ potential, we recomputed accommodation energies with the present model.…”

“…Energy order of three stable sites occupied by Yb in Ar were established from the lightand heat-induced site interconversion kinetics [10]. Of course, classical modeling is very helpful for trapping site characterization, especially if addresses kinetic [11,18] or thermodynamic [10,19] stability of the predicted sites. Fortunately, crystallographic intuition helps a lot.…”

“…In the present contribution we report on the computational search of the thermodynamically stable atomic trapping sites in the Ar crystal. As an atomistic model, we used the one proposed before [10,19]. It describes an ideal crystal, but provides enough flexibility for accommodating a guest in the vacancies of different volume.…”