Combined DFT and BS study on the exchange coupling of dinuclear sandwich-type POM: comparison of different functionals and reliability of structure modeling

Abstract

The exchange coupling of a group of three dinuclear sandwich-type polyoxomolybdates [MM'(AsMo7O27)2](12-) with MM' = CrCr, FeFe, FeCr are theoretically predicted from combined DFT and broken-symmetry (BS) approach. Eight different XC functionals are utilized to calculate the exchange-coupling constant J from both the full crystalline structures and model structures of smaller size. The comparison between theoretical values and accurate experimental results supports the applicability of DFT-BS method in this new type of sandwich-type dinuclear polyoxomolybdates. However, a careful choice of functionals is necessary to achieve the desired accuracy. The encouraging results obtained from calculations on model structures highlight the great potential of application of structure modeling in theoretical study of POM. Structural modeling may not only reduce the computational cost of large POM species but also be able to take into account the external field effect arising from solvent molecules in solution or counterions in crystal.

Are trinuclear superhalogens promising candidates for building blocks of novel magnetic materials? A theoretical prospect from combined broken-symmetry density functional theory and ab initio study

“…Therefore, novel magnetic materials are clearly a brand-new research direction of superhalogens. Encouragingly, positive progress in this direction has already been achieved because the coexistence of high stability and strong magnetic coupling has been verified by our recent work of combined density functional theory 26 and broken-symmetry [27][28][29][30][31][32][33][34][35][36] (DFT-BS) study of dinuclear TM-based superhalogens. 22 In pursuit of further advance in this direction, a series of 18 TM-based trinuclear superhalogen anions [M 3 X 7 ] − (M = Mn II , Tc II , and X = F − , Cl − , Br − ) is investigated in this work.…”

“…1) in which the localization of β spin trinuclear system All the calculations are performed with Gaussian 03 program 78,79 and the initial guesses for the construction of BS state are generated with NBO 5.0 code. 22,36,[80][81][82][83] The geometric stabilities of the optimized structures are examined via vibrational analysis 79 (Table S1 of the supplementary material 77 ). The wavefunctions of both HS and BS states are tested with STABLE = OPT option 79 to ensure the reliability of our calculations.…”

The magnetic coupling in manganese-based dinuclear superhalogens and their analogues. A theoretical characterization from a combined DFT and BS study

“…26,30 However, the direct application of eqn ( 2) is nearly impractical because the calculations of the intermediate or low spin state are usually problematic at the DFT level. 21 The BS technique, [22][23][24] developed by Noodleman and co-workers, has been proven to be the most commonly used method to solve this difficulty 27 as shown by its successful applications in TM systems, [32][33][34][35][36][37][38][39][40][41][42] organic diradicals [43][44][45][46] and hybrid systems consisting of both TM ions and organic radicals. [47][48][49] The BS state is monodeterminantally constructed to have opposite spins essentially localized on different magnetic centers and thus it breaks the spatial symmetry in the aspect of spin density distribution.…”

“…50,51 Therefore, a careful choice of functionals is definitely not trivial as shown by one recent report of striking differences between DFT-BS results of pure and hybrid functionals. 42,52 According to our best knowledge, a systematic and comprehensive comparison among different functionals is still absent for superhalogens. Therefore six different functionals, consisting of B3LYP, [53][54][55] O3LYP, 55,56 MPW1PW91, [57][58][59] BLYP, 53,55 OLYP 55,56 and PW91, 58,59 are examined in this work.…”

“…All the calculations are performed with the Gaussian 03 program 64,65 and the initial estimates for the construction of the BS state are generated with the NBO 5.0 code. 42,66,67 The wavefunctions of both HS and BS states are tested with the STABLE = OPT option 65 to ensure the reliability of our calculations.…”