A DMC study on FePc electronic state

We performed fixed-node DMC calculations on an isolated FePc [Iron(II) Phthalocyanine] using CASSCF nodal surfaces, getting its ground state, $^3A_{2g}$ [$d^2_{z^2}d^{2}_{xz,yz}d^{2}_{xy}$]. Virial ratios for each state are achieved to be within 0.042\% around 2.0. Recent studies [1] are proposing a mixed state with $^3E_g(b)$ and $^3B_{2g}$ as the ground state, while past ab-initio calculations [2] are predicting $^3A_{2g}$ or $^3E_g(a)$, giving still controversial arguments even within isolated/no-LS coupling model. Under $D_{4h}$ ligand field parameter space, ($10D_q$, $D_t$, $D_s$), the state, $^3A_{2g}$, is reported to be possible as a ground state [3], while it is not when we restrict the space into 2-dim sub-space corresponding to more specified symmetry as in FePc with plane square alignment of neighboring N to Fe ('superposition model' [4]). Our optimized geometry also satisfies the same symmetry, and hence appears to be contradicting to the ligand theory[4]. [1] J. Fern\'{a}ndez-Rodr\'{i}guez {\it et al.}, Phys. Rev. B {\bf 91}, 214427 (2015). [2] K. Nakamura {\it et al.}, Phys. Rev. B {\bf 85}, 235129 (2012). [3] P.S. Miedema {\it et al.} , J. Phys.: Conf. Ser. {\bf 190} , 012143 (2009). [4] M.D. Kuz’min {\it et al.} , J. Chem. Phys. {\bf 138} , 244308 (2013).