Long-range corrected density functional theory study on static second hyperpolarizabilities of singlet diradical systems
Long-range corrected density functional theory study on static second hyperpolarizabilities of singlet diradical systems
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DOI：
10.1063/1.3332707
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发表时间：
2010-03-07
影响因子：
4.4
通讯作者：
Tsuneda, Takao
中科院分区：
文献类型：
--
作者：
Kishi, Ryohei;Bonness, Sean;Tsuneda, Takao
在自旋不受限制的密度泛函理论(DFT)中，结合Becke-Lee-Yang-Parr交换相关泛函的长程修正(LC-UBLYP)方法被用于计算日益复杂的开壳单重态双自由基体系的第二超极化率(Gamma)，并表现出良好的性能：(I)对于最简单的H-2离解模型，LC-UBLYP方法计算的伽马值明显超过全组态相互作用结果，但定性地再现了伽马作为偶自由基性质的函数的演化；(Ii)对于小的单重态双自由基1，3偶极体系，通过LC-UBLYP方法半定量地再现了由UCCSD和UCCSD(T)参考方法确定的伽马的双基特征依赖关系，除了在自旋无限制解与自旋受限解重合的小的双基特征区域外，(Iii)LC-UBLYP方法还紧密地再现了UCCSD(T)关于对奎诺二甲烷模型体系的伽马的双基特征依赖的结果，特别是在中等和大的双基特征区域，而它显示了源于三重态不稳定性的接近0.2的双基特征(Y)的突变，(Iv)对于具有中等和大双自由基特征的开壳单重态体系，LC-UBLYP重现参考耦合团簇结果的可靠性也已在1，4-bis-(imidazol-2-ylidene)-cyclohexa-2，5-diene(Bi2Y)的情况下得到证实，然后(V)对于由一对由共轭连接物分隔的苯基建立的真实体系，LC-UBLYP的结果被发现与UBHandHLYP值非常接近--对于小的体系，这与用相关分子轨道方法得到的值很好地一致--而UB3LYP的结果可能有很大的不同。这些结果不仅从有效确定开壳单重态系统的非线性光学性质的角度来看是重要的，而且从定义改进的交换关联泛函的新挑战的角度来看也是重要的。
Within the spin-unrestricted density functional theory (DFT) the long-range correction (LC) scheme combined with the Becke-Lee-Yang-Parr exchange-correlation functional, referred to as LC-UBLYP method, has been applied to the calculation of the second hyperpolarizability (gamma) of open-shell singlet diradical systems of increasing complexity and has demonstrated good performance: (i) for the simplest H-2 dissociation model, the gamma values calculated by the LC-UBLYP method significantly overshoot the full configuration interaction result but reproduce qualitatively the evolution of gamma as a function of the diradical character, (ii) for small singlet diradical 1,3-dipole systems, the diradical character dependence of gamma determined by the UCCSD and UCCSD(T) reference methods is reproduced semiquantitatively by the LC-UBLYP method except in the small diradical character region, where the spin-unrestricted solutions coincide with spin-restricted solutions, (iii) the LC-UBLYP method also closely reproduces the UCCSD(T) results on the diradical character dependence of gamma of the p-quinodimethane model system, particularly in the intermediate and large diradical character regions, whereas it shows an abrupt change for a diradical character (y) close to 0.2 originating from the triplet instability, (iv) the reliability of LC-UBLYP to reproduce reference coupled cluster results on open-shell singlet systems with intermediate and large diradical characters has also been substantiated in the case of gamma of 1,4-bis-(imidazol-2-ylidene)-cyclohexa-2,5-diene (BI2Y), then (v), for real systems built from a pair of phenalenyl radicals separated by a conjugated linker, the LC-UBLYP results have been found to closely match the UBHandHLYP values-which, for small systems are in good agreement with those obtained using correlated molecular orbital methods-whereas the UB3LYP results can be much different. These results are not only important from the viewpoint of an efficient determination of the nonlinear optical properties of open-shell singlet systems, but also from the viewpoint of defining new challenges for elaborating improved exchange-correlation functionals.