密度泛函理论在分子磁学中的应用

通过对桥联双核铁的磁耦合常数的计算，探讨了密度泛函理论计算条件对计算 结果的影响。基于密度泛函理论下的破损态方法，着重讨论了双核 Fe(III)_2的 d~5-d~5电子通过氧桥的超交换作用。研究发现分子的反铁磁通道主要是Fe(III) d_yz和d_z~2与μ-O的p轨道形成的，具有π*/π*和σ*/σ*特征的超交换通道。     

砷原子团簇结构的量子化学密度泛函理论研究

采用密度泛函理论的三种方法:局域自旋密度近似SVWN、梯度修正BLYP、杂化密度泛函B3LYP,优化了中性Asn、负离子Asn-(n=2～5)的结构,在优化结构基础上计算了它们的振动光谱,获得它们稳定的最低能量态的结构.其中中性Asn(n=2～5)的稳定结构的计算结果,与已有的理论结果以及实验数据进行了比较.而对负离子Asn-(n=2～5))的稳定结构作了预言.同时计算了Asn(n=2～5)的绝热电子亲和能(EAa),与有关光电子谱学的实验值符合较好.     

密度泛函理论在分子磁学中的应用

通过对桥联双核铁的磁耦合常数的计算，探讨了密度泛函理论计算条件对计算 结果的影响。基于密度泛函理论下的破损态方法，着重讨论了双核 Fe(III)_2的 d~5-d~5电子通过氧桥的超交换作用。研究发现分子的反铁磁通道主要是Fe(III) d_yz和d_z~2与μ-O的p轨道形成的，具有π*/π*和σ*/σ*特征的超交换通道。     

镱硫属化合物的密度泛函理论研究

用密度泛函理论(DFT)研究镱硫属化合物的电子结构和性质,通过与实验比较考察了现有的几种近似密度泛函公式对镧系元素化合物的适用程度和相对论效应的影响.结果表明,用DFT计算的YbO键长对实验值的偏差约为0.002nm;但得到的键能即使在考虑梯度校正和相对论效应之后,仍比实验值高,在定域密度近似基础上引入交换梯度校正使键能计算值减小,其中PW86x使键能计算值减小稍多些,结果更接近实验值;相关梯度校正使键能计算值升高.相对论效应使键长缩短0.004～0.006nm,键能减小约0.5eV.计算结果的分析表明,Yb的5d轨道和配体的np轨道间形成σ键和π键.在所研究的分子体系中,配体原子从O到Te、Yb原子的5d轨道布后数依次减少,同键能减弱的顺序一致.相对论效应使键能减小的主要原因是在成键过程中发生了Yb的6s电子向5d轨道的转移,而相对论效应使该过程能量增加.偶极矩和电荷分布的计算表明,Yb-L键以共价性为主,相对论效应使共价性成份增加.     

立方烷型四核IB族金属-钨簇合物电子结构的从头算研究

采用从头算方法和自然成键轨道分析对双核鹤硫簇合物[W2S4（SH2）2]2-和立方烷型四核异金属鸽硫簇合物W2MM’（SH2）2（PH3）Cu2,Ag2,CuAg）的电子结构进行研究。研究结果表明，钨簇合物与相簇合物具有相似的电子结构特征，金属原子间均存在不同程度的直接成键和通过桥原子或端原子的明显的多中心d-pπ键，还讨论了这种多中心镇对于簇加成反应及簇合物稳定性的影响。     

过渡金属混合簇Nb2Rh2的密度泛函研究

采用密度泛函方法(DFT)研究了过渡金属混合簇Nb_mRh_n (m, n≤2) 的结构、稳定性规律及它们的成键情况. 结果表明, Nb—Nb键较强, Rh—Rh键较弱, 而Nb—Rh键的强度则介于两者之间. 在Nb₂Rh₂直线和折线构型中, 金属键有强弱交替的现象. Nb₂Rh₂的各种构型在自旋多重度较小时稳定.     

过渡金属混合簇Nb2Rh2的密度泛函研究

采用密度泛函方法(DFT)研究了过渡金属混合簇Nb_mRh_n (m, n≤2) 的结构、稳定性规律及它们的成键情况. 结果表明, Nb—Nb键较强, Rh—Rh键较弱, 而Nb—Rh键的强度则介于两者之间. 在Nb₂Rh₂直线和折线构型中, 金属键有强弱交替的现象. Nb₂Rh₂的各种构型在自旋多重度较小时稳定.     

Au_n团簇催化水煤气变换反应机理的密度泛函理论研究

利用密度泛函理论(DFT)研究了Au10、Au13和Au20三类团簇的稳定性和对水煤气变换(WGSR)反应的催化活性,考察了各物质在Aun团簇上的吸附行为和微观反应机理。结果表明,三类Aun团簇的稳定性顺序为Au10Au13Au20,而Aun团簇中电子离域性及吸附能力大小趋势为Au13Au10Au20。在三类Aun团簇上,水煤气变换反应的控速步骤均为H2O的解离,但其反应机理路径有所不同。Au10团簇上为羧基机理,COOH*中间体直接解离;Au13团簇上为氧化还原机理,两个OH*发生歧化反应;Au20团簇上为羧基机理,COOH*和OH*发生歧化反应。通过对三类团簇上的最佳反应路径进行比较发现,Au13团簇在低温下具有较好的催化活性。     

黄酮类化合物的密度泛函理论研究

在混合密度泛函B3LYP理论下,用6-31G*基函数研究了几种典型黄酮类化合物分子的几何结构、电子结构和分子的静电势,讨论了电子结构和分子活性部位的关系.     

Ionic dissociations of chlorosulfonic acid in microsolvated clusters: A density functional theory and ab initio MO study

Ionic dissociation of chlorosulfonic acid (HSO3Cl) in the molecular clusters HSO3Cl-(H2O)n (n = 1-4) and HSO3Cl-NH3-(H2O)n (n = 0-3) was investigated by density functional theory and ab initio molecular orbital theory. The equilibrium structures, binding energies, and thermodynamic properties, such as relative enthalpy and relative Gibbs free energy, and were calculated using the hybrid density func- tional (B3LYP) method and the second order M?ller-Plesset approximation (MP2) method with the 6-311 G** basis set. Chlorosulfonic acid was found to require a minimum of three water molecules for ionization to occur and at least one water molecule to protonate ammonia. The corresponding clusters with fewer water molecules were found to be strongly hydrogen-bonded. The related properties and acid strength of chlorosulfonic acid were discussed and compared to the acid strengths of perchloric acid and sulfuric acid in the context of clusters with ammonia and water. The relative stabilities of these clusters were also investigated.     

Determination of spin-orbit coupling contributions in the framework of density functional theory

We present a noniterative method to calculate spin-orbit coupling by means of a theoretical approach that provides the use of the full Breit-Pauli operator. This method was applied to compute one and two-electron spin-orbit coupling contributions between singlet and triplet, and doublet and doublet states, respectively. These states have been represented by monodeterminantal wave functions and optimized using the PW91 gradient-corrected exchange-correlation functional and the hybrid B3LYP one. They have been supplied by the conventional density functional theory packages, and thus coupled by our spin-orbit coupling code. Different size basis sets have been employed and the obtained results have been compared with the corresponding ones provided by some of the already existing methods and with the experimental data. They have been found to be in good quantitative agreement.     

Study on electronic density topology of various cluster models of Mg/Al hydrotalcite by density functional theory

The geometry and electronic topology properties of Mg/Al hydrotalcite cluster models were comparatively investigated by means of density functional theory at GGA/DND levels. The results suggested that cluster model containing seven octahedral cations was the smallest size to be employed to simulate other properties. The fact that the n+ charge of cluster models containing n aluminum atoms can reflect electronic properties of anionic clay layer sheet. The bond lengths of clusters can be modified by terminating with or without OH~-/H_2O groups in terms of principle of bond order conservation.     

Density functional study of carbon monoxide adsorption on small cationic,neutral, and anionic aluminum nitride clusters

CO adsorption on small cationic, neutral, and anionic (AlN)_n (n = 1–6) clusters has been investigated using density functional theory in the generalized gradient approximation. Among various possible CO adsorption sites, an N on‐top (onefold coordinated) site is found to be the most favorable one, irrespective of the charge state of the clusters. The adsorption energies of CO on the anionic (AlN)_nCO (n = 2–4) clusters are greater than those on the neutral and cationic complexes. The adsorption energies on the cationic and neutral complexes reflect the odd–even oscillations, and the adsorption energies of CO on the cationic (AlN)_nCO (n = 5, 6) clusters are greater than those on the neutral and anionic complexes. The adsorption energies for the different charge states decrease with increasing cluster size. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Fractional occupation numbers and spin density functional calculations of degenerate systems

We implemented ab initio self‐consistent field (SCF) fractional occupation numbers (FON) calculation with Dunlap's interpolation scheme for the twisted ethylene, which is a prototype molecule of a σ–π biradical system. The calculational results are compared with those of complete‐active‐space (CAS) SCF and spin‐unrestricted Kohn–Sham (UKS) calculations on potential surfaces, occupation numbers of natural orbitals, and correlation entropies. It was found that the UKS methods gave similar results to CASSCF, while the FON solutions appeared in only the nearly complete degenerate region. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 93: 317–323, 2003     

Interaction of copernicium with gold: Assessment of applicability of simple density functional theories

Interactions of Cn (element 112) atom with small Au clusters are studied using accurate ab initio scalar relativistic coupled cluster method for correlation treatment and two‐component relativistic density functional theory (RDFT) to take account of spin‐dependent relativistic effects. The results demonstrate the failure of RDFT with simple generalized‐gradient and hybrid functionals in describing Cn–Au bonds in complex systems. © 2013 Wiley Periodicals, Inc.     

Energy landscapes of nucleophilic substitution reactions: a comparison of density functional theory and coupled cluster methods

We have carried out a detailed evaluation of the performance of all classes of density functional theory (DFT) for describing the potential energy surface (PES) of a wide range of nucleophilic substitution (SN2) reactions involving, amongst others, nucleophilic attack at carbon, nitrogen, silicon, and sulfur. In particular, we investigate the ability of the local density approximation (LDA), generalized gradient approximation (GGA), meta-GGA as well as hybrid DFT to reproduce high-level coupled cluster (CCSD(T)) benchmarks that are close to the basis set limit. The most accurate GGA, meta-GGA, and hybrid functionals yield mean absolute deviations of about 2 kcal/mol relative to the coupled cluster data, for reactant complexation, central barriers, overall barriers as well as reaction energies. For the three nonlocal DFT classes, the best functionals are found to be OPBE (GGA), OLAP3 (meta-GGA), and mPBE0KCIS (hybrid DFT). The popular B3LYP functional is not bad but performs significantly worse than the best GGA functionals. Furthermore, we have compared the geometries from several density functionals with the reference CCSD(T) data. The same GGA functionals that perform best for the energies (OPBE, OLYP), also perform best for the geometries with average absolute deviations in bond lengths of 0.06 A and 0.6 degrees, even better than the best meta-GGA and hybrid functionals. In view of the reduced computational effort of GGAs with respect to meta-GGAs and hybrid functionals, let alone coupled cluster, we recommend the use of accurate GGAs such as OPBE or OLYP for the study of SN2 reactions.     

Ionic dissociations of chlorosulfonic acid in microsolvated clusters: A density functional theory and ab initio MO study

Ionic dissociation of chlorosulfonic acid (HSO₃Cl) in the molecular clusters HSO₃Cl-(H₂O) _n (n = 1–4) and HSO₃Cl-NH₃-(H₂O) _n (n = 0–3) was investigated by density functional theory and ab initio molecular orbital theory. The equilibrium structures, binding energies, and thermodynamic properties, such as relative enthalpy and relative Gibbs free energy, and were calculated using the hybrid density functional (B3LYP) method and the second order M?ller-Plesset approximation (MP2) method with the 6-311++G** basis set. Chlorosulfonic acid was found to require a minimum of three water molecules for ionization to occur and at least one water molecule to protonate ammonia. The corresponding clusters with fewer water molecules were found to be strongly hydrogen-bonded. The related properties and acid strength of chlorosulfonic acid were discussed and compared to the acid strengths of perchloric acid and sulfuric acid in the context of clusters with ammonia and water. The relative stabilities of these clusters were also investigated. Supported by the National Natural Science Foundation of China (Grant No. 20273046), the Camille and Henry Dreyfus Foundation (Award No. TH-00-028) of California State University, Fullerton, and the Younger Teacher Foundation of Suzhou University (Grant No. Q31094040)