气相中呋喃负离子与N2O反应机理的理论研究

采用QCISD和MP2两种计算方法,在6-31＋＋G(d,p)的基组下,对气相中呋喃负离子与N2O反应的微观机理进行了较为系统的计算研究。结果表明,通道1中的路径1和2为此反应体系的主反应路径,其各反应驻点的能量均低于反应物的,并且互为竞争路径。主要产物为C4H3NO- 和NO,同时也应能检测到少量的C4H3O2- 和N2。理论计算结果与实验预测基本一致。此外,对于次要路径也做了简要说明,并且此反应体系的所有反应路径均为强放热过程。     

An improved algorithm for analytical gradient evaluation in resolution-of-the-identity second-order Møller-Plesset perturbation theory: application to alanine tetrapeptide conformational analysis

We present a new algorithm for analytical gradient evaluation in resolution‐of‐the‐identity second‐order Møller‐Plesset perturbation theory (RI‐MP2) and thoroughly assess its computational performance and chemical accuracy. This algorithm addresses the potential I/O bottlenecks associated with disk‐based storage and access of the RI‐MP2 t‐amplitudes by utilizing a semi‐direct batching approach and yields computational speed‐ups of approximately 2–3 over the best conventional MP2 analytical gradient algorithms. In addition, we attempt to provide a straightforward guide to performing reliable and cost‐efficient geometry optimizations at the RI‐MP2 level of theory. By computing relative atomization energies for the G3/99 set and optimizing a test set of 136 equilibrium molecular structures, we demonstrate that satisfactory relative accuracy and significant computational savings can be obtained using Pople‐style atomic orbital basis sets with the existing auxiliary basis expansions for RI‐MP2 computations. We also show that RI‐MP2 geometry optimizations reproduce molecular equilibrium structures with no significant deviations (>0.1 pm) from the predictions of conventional MP2 theory. As a chemical application, we computed the extended‐globular conformational energy gap in alanine tetrapeptide at the extrapolated RI‐MP2/cc‐pV(TQ)Z level as 2.884, 4.414, and 4.994 kcal/mol for structures optimized using the HF, DFT (B3LYP), and RI‐MP2 methodologies and the cc‐pVTZ basis set, respectively. These marked energetic discrepancies originate from differential intramolecular hydrogen bonding present in the globular conformation optimized at these levels of theory and clearly demonstrate the importance of long‐range correlation effects in polypeptide conformational analysis. © 2007 Wiley Periodicals, Inc. J Comput Chem, 2007     

Theoretical Comparison of the Linear and Bent Structures for the Weakly Bound CO2—HF Complex

Density‐functional theory method (DFT) B3LYP/6–311++G(3df,2pd) and Moller‐Plesset perturbation method (MP2) MP2/6–311++G(3df,2pd) of Gaussian 03 were selected for the theoretical study of weakly bound CO₂—HF complex. In addition to the well‐known linear structure, the various bent structure complexes were also found in this work. The self‐consistent energy differences were only around 0.02 kJ/mol between the bent structure and linear structure by comparison. From the results of H‐bonding distance, dHF elongation and red shift of VHF vibration frequency, all the evidence shows that the H‐bonding effect in the bent structure is stronger than the linear structure. However, if one compares the Gibbs energy of the complex formation by temperature variation, it is very easily found that the linear form is favored under the thermal conditions of most temperatures whenever T ≥ 40 K. Such a fact is consistent with the former spectroscopic observed result of Klemperer et al.     

Two-level hierarchical parallelization of second-order Møller-Plesset perturbation calculations in divide-and-conquer method

A two‐level hierarchical parallelization scheme including the second‐order Møller–Plesset perturbation (MP2) theory in the divide‐and‐conquer method is presented. The scheme is a combination of coarse‐grain parallelization assigning each subsystem to a group of processors, with fine‐grain parallelization, where the computational tasks for evaluating MP2 correlation energy of the assigned subsystem are distributed among processors in the group. Test calculations demonstrate that the present scheme shows high parallel efficiency and makes MP2 calculations practical for very large molecules. © 2011 Wiley Periodicals, Inc. J Comput Chem, 2011     

Hydrogen bonding in the mixed HF/HCl dimer: Is it better to give or receive?

The ClH⋯FH and FH⋯ClH configurations of the mixed HF/HCl dimer (where the donor⋯acceptor notation indicates the directionality of the hydrogen bond) as well as the transition state connecting the two configurations have been optimized using MP2 and CCSD(T) with correlation consistent basis sets as large as aug‐cc‐pV(5 + d)Z. Harmonic vibrational frequencies confirmed that both configurations correspond to minima and that the transition state has exactly one imaginary frequency. In addition, anharmonic vibrational frequencies computed with second‐order vibrational perturbation theory (VPT2) are within 6 cm⁻¹ of the available experimental values and deviate by no more than 4 cm⁻¹ for the complexation induced HF frequency shifts. The CCSD(T) electronic energies obtained with the largest basis set indicate that the barrier height is 0.40 kcal mol⁻¹ and the FH⋯ClH configuration lies 0.19 kcal mol⁻¹ below the ClH⋯FH configuration. While only modestly attenuating the barrier height, the inclusion of either the harmonic or anharmonic zero‐point vibrational energy effectively makes both minima isoenergetic, with the ClH⋯FH configuration being lower by only 0.03 kcal mol⁻¹. © 2018 Wiley Periodicals, Inc.