Jahn–Teller effect in the magnesium phthalocyanine anion

Abstract

We present an ab initio study of the static Jahn–Teller (JT) effect in the magnesium phthalocyanine anion (MgPc −). The neutral MgPc has D 4 h symmetry with a doubly degenerate e g affinity level and 14 B 1g plus 14 B 2g JT active modes. MgPc − is thus a physical realization of a e g ⊗ (B 1g ⊕ B 2g) JT problem. We carried out a first principles DFT/LDA calculation of the electronic structure, full vibrational spectrum, and linear electron–vibration coupling constants for this system. From that we calculate a static JT energy gain of 50 meV – essentially due to a B 1g distortion – characterizing this as a relatively weak-coupling system. It is anticipated that quantum mechanical dynamic JT tunneling between the two equivalent B 1g distorted JT minima should be quite important. Two B 2g distorted saddle points are identified as the relevant transition states, with a barrier of 27 meV above the minima. Previous work on this JT problem is also addressed.