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In this study, the zero-field splitting parameters ( D , E ) and effective exchange integrals ( J ) for a Mn 12 /Mn 11 Cr mixed crystal were evaluated using ab initio molecular orbital (MO) computations based on the hybrid density functional theory (DFT) methods for Mn 11 Cr ∗ -acetate cluster (Mn 12 and Mn 11 Cr mixing). In this study, Mn 12 -acetate, Mn 11 Cr-acetate, and Mn 12− n Cr n -acetate clusters were focused on. The zero-field splitting (ZFS) parameters are obtained by UB3LYP methods, i.e. −0.339 cm −1 (Mn 12 -acetate) and −0.351 cm −1 (Mn 11 Cr-acetate). The energy barriers were estimated to be 53.7 K and 50.4 K, which showed good agreement with previously reported experimental values of 68.8 K and 56.8 K, respectively. The origin of such anisotropy is assumed to be the eight Mn III ions with d 4 -electrons in their outer ring subunits, where elongated conformation along the axial direction becomes very important and leads to negative D values. The spin networks in these clusters were discussed by using the effective exchange integral sets. The J s value, as estimated by the UB3LYP method revealed that the J 2 , J 3 , and J 3 ′ interactions played important roles in describing the parallel spin ordering in cubane and ring subunits as well as the antiferromagnetic coupling between two subunits. The other interactions, i.e. J 1 , J 1 ′, J 4 , and J 4 ′ somewhat disturbed the spin ordering in the Mn 12 -acetate cluster. The substitution of Mn IV by Cr III did not change the spin network. However, the total S value changed after the substitution. [ABSTRACT FROM AUTHOR]

Abstract: The effective exchange integrals (J(HB)) of the Heisenberg spin model have been evaluated by using the ab initio MO and based on Hartree–Fock (HF) and density functional theory (DFT) for organic magnetic metals, the (EDT-TTFVO)2FeBr4 crystal based on the X-ray crystallographic structures at 113K. In order to study the magnetic properties, we proposed some of the pairs, where the direct (d–d) and indirect (d–π–d) magnetic couplings between Fe(III) d-spins (S =5/2) without/with π-dimer spins (S =1/2) were calculated, respectively. The effective exchange integrals were evaluated by using UB3LYP method, and principal J values were 0.5, −0.1 and 0.4K. From these results, it is found that there were three dimensional spin arrangements of Fe(III) d-spins. The Quantum Monte Carlo (QMC) simulations had been carried out with our calculated J values to evaluate the magnetic susceptibility for this molecular crystal, reproducing the experimental tendency. [Copyright &y& Elsevier]

Effective exchange integral (Jab) values calculated by cluster models were compared with values calculated under the periodic boundary conditions. So far, to estimate the Jab value of a macro system, we have considered that of the corresponding to cluster one. However, they will get absolutely nothing out of it if a cluster model and the periodic boundary conditions method give different results to us. The main aim of this report is to give an opinion to this issue using a one-dimensional polyhydrogen system as example. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [ABSTRACT FROM AUTHOR]

Inter-dimer magnetic interactions (J ab(D) ) between (BEDT-TTF) 2 + • dimers in the κ-(BEDT-TTF) 2 Cu 2 (CN) 3 crystal has been studied theoretically. In these crystals, triangular lattice structure with spin frustration has been discovered and experimental studies have been performed by several research groups. We have calculated the inter-dimer J ab(D) values by using several methods. In addition, we have analyzed the spin lattice with optimization of θ angle in classical Heisenberg spin model and with numerical diagonalization in quantum Heisenberg spin model. [ABSTRACT FROM AUTHOR]

Abstract: Inter-dimer magnetic interactions (J ab(D)) between BETS donors in the κ-BETS2FeCl4 crystal were studied theoretically by using of ab initio MO and DFT methods. These interaction parameters can describe spin properties. In cluster of four BETS molecules with two holes, more accurate J ab(D) values were evaluated directly, though such J ab(D) values were already evaluated from inter-molecular magnetic interaction (J ab(M)) with the approximate equation J ab(D) = J ab(M)/2. In cluster of six molecules with three holes, competition of three antiferromagnetic interaction was discussed. Necessity of calculation under periodic condition and for surrounding cluster was introduced. [Copyright &y& Elsevier]

Abstract: In order to inquire into the mechanism of the change in the magnetism of spiro-biphenalnyls, intermolecular magnetic interaction has been investigated in terms of the effective exchange integral of the Heisenberg model for dimeric pairs of diethyl-substituted spiro-biphenalenyl. Variation of the magnetic interaction with respect to temperature has been evaluated for X-ray crystallographic structures at several temperature points by Kohn–Sham hybrid-DFT. The intermolecular magnetic interactions have been calculated for the π-dimers to be antiferromagnetic at each temperature, which has decreased by approximately 30% in the magnitude from 100 to 173K. In addition, the interactions have been almost none at 100 and 173K except for one pair and the remaining pair had ferromagnetic interaction. Therefore, it has been found that the change in their magnetism is understood by the formation of a ferromagnetic dimer-pair at 173K. Moreover, the natural orbital analysis for the electronic structure of diethyl-substituted spiro-biphenelenyl has shown our solutions are essentially identified to Haddon’s proposal in terms of the valence bond picture. [Copyright &y& Elsevier]

Theoretical calculations of ab initio molecular orbital and density functional theory calculations were carried out in order to investigate magnetic interaction in one‐dimensional spin chains. Effective exchange integral (Jab) values are useful parameters in studying magnetic interaction in spin systems. Chemical indices also were evaluated to represent stability of broken symmetry spin. For one set of spin chains, alignment of hydrogen atoms as the most simple organic cluster was employed. Number of H atoms in employed models is two and 50 with interatomic distance 2.1 Å. In addition, copper bromide chains (CunBrm) were also studied. Simple molecules Br2‐Cu‐Br2‐Cu‐Br2 (without apical‐Br) and Br2‐CuBr‐Br2‐CuBr‐Br2 (with apical‐Br) were employed for simple model structure. Four parameters (r, a, b, and c) can fix the structure and study parameter dependency of Jab values. For experimental studies, Sugimoto and his coworkers have reported synthesis and experimental studies for complex of both CunBrm chains and TTF‐derivative donor. Magnetic behavior in only CunBrm chains was investigated in detail by several ab initio methods. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004 [ABSTRACT FROM AUTHOR]

Intermolecular magnetic interaction of some donors, i.e. BEDT-TTF, BETS, TMTTF and TMTSF, in some organic superconductive crystals were studied theoretically by using ab initio MO and DFT methods. In addition, donor arrangements in both κ- and λ-phases crystals are also focused. For this purpose we employed κ-BETS2FeCl4 and λ-BETS2FeCl4 crystals for BETS salts; κ-(BEDT-TTF)2Cu[N(CN)2]X (X=Cl, Br and I) and κ-(BEDT-TTF)2Cu(NCS)2 crystals for BEDT-TTF salts; TMTTF2PF6 and TMTSF2PF6 crystals for TMTTF and TMTSF salts. For these systems all the effective exchange integral (Jab) values between two donors and between donor and counter anions were successfully evaluated. In addition the other effective parameters (tab, Ueff) were also obtained. Finally relationship between integral pair (J, J′) and transition temperature (TSC) was discussed. The two- and one-dimensional magnetic networks are essential for these crystals. [Copyright &y& Elsevier]

Abstract: In the κ-(BETS)2FeCl4 crystal as one of organic magnetic-metal crystals, localized spins of d-orbitals in anions is expected to play an important role to magnetic properties. To investigate all the magnetic interactions between neighboring two anions, various spatial conformation of dimers were assumed and studied. For variety of configurations of anion dimers, the values of effective exchange integral (J) in the Heisenberg spin model were calculated by using ab initio MO methods. It was found that very weak ferromagnetic interaction existed in a certain conformation, though antiferromagnetic interaction was reproduced in most of all conformations. [Copyright &y& Elsevier]

Stable carbene:bis(9-(10-phenyl)anthryl)carbene and model carbenes of which have been investigated by ab initio MO and Crystal orbital calculations. By hybrid density-functional calculation (B3LYP/4-31G) the carbene has character as a triplet carbene than a triplet diradical. Based on calculations on this carbene, a polycarbene is contrived to investigate interactions of carbenes, which are stabilized by aromatic rings. They have interacted with each other in antiferromagnetic fashion by both B3LYP MO and Crystal orbital calculations. Their magnetic interactions have been varied as the conformational changes of the aromatic rings, which have been evaluated by the effective exchange integral J(AP) based on the Heisenberg Hamiltonian. To describe the behavior AO-approach has been introduced and has worked efficiently. [Copyright &y& Elsevier]

Ab initio MO and hybrid-DFT calculations have been carried out by using model clusters; a [(NH3)2]+nn for pure organic conductors and b [H2NO&z.sbnd;(NH3)2]+nn for pure organomagnetic conductors. The results have shown that these models are reliable for investigation of intrinsic electronic states of magnetic/conductive organic compounds in detail by quantum chemical methods. [Copyright &y& Elsevier]

Abstract: Donor-radical model systems for chemical or photo-induced magnets are proposed, and their electronic states and intramolecular magnetic interactions are investigated by Kohn-Sham hybrid density functional theory (KS-HDFT). 5,10-dihydrophenazine is employed as a donor and nitronyl- or imino-nitroxide radicals as stable radical substituents. The models mostly provide ferromagnetic intramolecular spin alignment in hole doping. In addition, the inductive effect on intramolecular magnetic interactions is examined by substituting the 5- and 10-positions of dihydrophenazine by several electron-withdrawing and -donating groups. The model compounds exhibit appropriate magnetic interactions and ionization potentials to allow them to serve as components of chemical or photo-induced magnets. [Copyright &y& Elsevier]