Our calculated results demonstrate that the transition between the lowspin (LS) and high-spin (HS) states of these Fe2+ molecules is accompanied with redistribution of atomic charge and reformation of molecular orbitals. These cause differences in the kinetic energy, the electrostatic energy as well as the total energy between the LS and HS states. The LS state is advantage in the kinetic energy in comparison to the HS state, while the HS state is advantage in the electrostatic energy. Moreover, the coulomb attraction energy between the Fe2+ ion and its surrounding anionic ions plays a crucial role for spin crossover occurring. | Communications in Physics, Vol. 22, No. 4 (2012), pp. 309-316 GEOMETRIC STRUCTURE, ELECTRONIC STRUCTURE, AND SPIN TRANSITION OF Fe2+ SPIN-CROSSOVER MOLECULES NGUYEN VAN THANH, NGUYEN THI NGUYET ANH, AND NGUYEN ANH TUAN Faculty of Physics, Hanoi University of Science, Vietnam National University, Hanoi Abstract. We present a density functional study on the geometric structure, electronic structure and spin transition of a series of Fe2+ spin-crossover molecules, ., [Fe(abpt)2 (NCS)2 ] (1), [Fe(abpt)2 (NCSe)2 ] (2), and [Fe(abpt)2 (C(CN)3 )2 ] (3) with abpt = 4-amino-3,5-bis(pyridin-2-yl)1,2,4-triazole in order to shed light on more about the dynamics of the spin-crossover phenomenon. All results presented in this study were obtained by using the exchange correlation PBE functional. For better accuracy, the hexadecapolar expansion scheme is adopted for resolving the charge density and Coulombic potential. Our calculated results demonstrate that the transition between the lowspin (LS) and high-spin (HS) states of these Fe2+ molecules is accompanied with redistribution of atomic charge and reformation of molecular orbitals. These cause differences in the kinetic energy, the electrostatic energy as well as the total energy between the LS and HS states. The LS state is advantage in the kinetic energy in comparison to the HS state, while the HS state is advantage in the electrostatic energy. Moreover, the coulomb attraction energy between the Fe2+ ion and its surrounding anionic ions plays a crucial role for spin crossover occurring. I. INTRODUCTION Transition metal complexes that exhibit a temperature dependent crossover from a low-spin (LS) state to a high-spin (HS) state have been prepared as early as 1908 [1]. In the last few decades, research into the preparation and properties of complexes that exhibit this effect has been extensive after it was discovered that spin state can be switched reversibly by pressure or light irradiation in solid samples [2] as well
