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Benchmark relative energies for large water clusters with the generalized energy-based fragmentation method

Benchmark relative energies for large water clusters with th...

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第十三届全国量子化学会议

作者： Dandan Yuan Yunzhi Li Zhigang Ni Peter Pulay Wei Li Shuhua Li School of Chemistry and Chemical Engineering Key Laboratory of Mesoscopic Chemistry of Ministry of EducationInstitute of Theoretical and Computational ChemistryNanjing University Department of Chemistry and Biochemistry University of Arkansas

The generalized energy-based fragmentation（GEBF） method has been applied to investigate relative energies of large water clusters（H2O）n（n=32, 64）with the coupled-cluster singles and doubles with noniterative triple excitations（CCSD（T）） and second-order M鴏ler-Plesset perturbation theory（MP2） at the complete basis set（CBS） limit. Here large water clusters are chosen to be representative structures sampled from molecular dynamics（MD） simu lations of liquid water. Our calculations show that the GEBF method is capable of providing highly accurate relative energies for these water clusters in a cost-effective *** demonstrate that the relative energies from GEBF-MP2/CBS are in excellent agreement with those from GEBF-CCSD（T）/CBS for these water clusters. With the GEBF-CCSD（T）/CBS relative energies as the benchmark results, we have assessed the performance of several theoretical methods widely used for ab initio MD simulations of liquids and aqueous solutions. These methods include density functional theory（DFT） with a number of different functionals, MP2, and density functional tight-binding（the third generation, DFTB3 in short）. We find that MP2/aug-cc-pVDZ and several DFT methods（such as LC-ωPBE-D3 and ωB97XD）with the aug-cc-pVTZ basis set can provide satisfactory description for these water clusters. Some widely used functionals（such as B3 LYP, PBE0） and DFTB3 are not accurate enough for describing the relative energies of large water cl *** the basis set dependence of DFT is less than that of ab initio electron correlation methods, we recommend the combination of a few best functionals and large basis sets（at least aug-cc-pVTZ） in theoretical studies on water clusters or aqueous solutions.

关键词： generalized energy-based fragmentation method water clusters relative energies electron correlation density functional theory

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Understanding Polymorphism-Dependent Emission Properties of Molecular Crystals with a Refined QM/MM Approach

Understanding Polymorphism-Dependent Emission Properties of ...

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第十三届全国量子化学会议

作者： Yunzhi Li Guoqiang Wang Wei Li Yue Wang Shuhua Li School of Chemistry and Chemical Engineering Key Laboratory of Mesoscopic Chemistry of Ministry of EducationInstitute of Theoretical and Computational ChemistryNanjing University State Key Laboratory of Supramolecular Structure and Materials College of ChemistryJilin University

An efficient quantum mechanical/molecular mechanics（QM/MM） approach is developed for investigating polymorphism-dependent emission properties of molecular crystals. In this approach, we proposed a simple and effective way of automatically building cluster models（as the QM region） for the general QM/MM approach to deal with the excited states of molecular crystals. This approach is then applied to understand the polymorphism-dependent emission properties of two organic crystals comprised of 3（5）-（9-anthryl）pyrazole and its isomeride. Our results demonstrated that a monomer model for QM/MM calculations is suitable for describing the emission spectra of the crystal without the π…π stacking *** for the crystal with the notable intermolecular π…π stacking interaction, the most stable trimer model（or at least the most stable dimer model） should be used for accurately describing the corresponding emission spectra. The effect of the π…πstacking interaction on the emission properties of crystals can be understood by the fact that the intermolecular π…π interactions can significantly reduce the energy gap between frontier molecular orbitals of molecular clusters（dimers or trimers）. The results from the present work provide useful guidelines for understanding and designing the luminescent materials.

关键词： Organic polymorphs emission energies time-dependent density functional theory quantum mechanics/molecular mechanics method generalized energy-based fragmentation method

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