Accuracy Of Potential Energy Surfaces Research Articles

A theoretical study of the intermolecular interactions of H2–CuF complex: Intermolecular vibrations, isotope effects, and rotational structure

In this paper, a theoretical study has been made on the intermolecular interactions of the H2–CuF complex, including binding energy, intermolecular vibrations, isotope effects, and rotational structure. Based on different bond lengths of H2 and CuF monomers, three intermolecular potential energy surfaces (PESs) were constructed at the level of single and double excitation coupled-cluster method with a non-iterative perturbation treatment of triple excitations [CCSD(T)] with aug-cc-pVTZ basis set supplemented with bond functions. A global minimum on the PESs show that H2–CuF complex belongs to C2ν point group with a T-shaped structure. The obtained binding energy ranges from 8890 to 10050 cm−1, which increases as the increment of H–H bond length, but opposite case has been determined as the increment of Cu–F bond length. The accuracy of PESs was examined by the available data of 101–000 transition. The predicted rotational transition frequency obtained from bound state calculations can reproduce the experimental observation very well, and the predicted error is 0.1% based on the PES1 constructed with rH2 and rCuF fixed at 0.838 and 1.7409 Å. By analyzing the wave function of the bound state, the intermolecular vibrational modes were assigned unambiguously. Isotope effects were also studied and the largest error is also 0.1% compared with the available 101–000 transition data. A set of spectroscopic parameters were obtained for six isotopologues to determine rotational structure of H2–CuF complex. Upon the complex formation, the obtained structure parameters show that H–H bond length is elongated by 0.081 Å, while Cu–F value is shortened by 0.008 Å from the respective average bond lengths of free monomer.

New potential energy surfaces for the complexes Ar–CuX (X = F, Cl, Br, and I)

New intermolecular potential energy surfaces (PESs) are constructed at the level of the non-iterative perturbation treatment of triple excitations [CCSD(T)] plus aug-cc-pVQZ basis set supplemented with bond functions for the complexes Ar–CuX (X = F, Cl, Br, and I) at the rigid rotor approximation. The global minimum is assigned to be a collinear Ar–Cu–X geometry, while the local minimum is an anti-linear Cu–X–Ar geometry on the PES for each complex. Based on the PESs, the intermolecular vibrations, pure rotational spectra, as well as isotope effects are investigated via the bound state calculations. We also give a detailed comparison of the structural parameters, binding energies, accuracy of PESs, as well as the results of basis set superposition error (BSSE) correction with those of Ar–AgX complexes. In addition, we construct a three-dimension (3D) intermolecular PES for the complex Ar–CuF, which not only gives the information of structural change for Cu―F distance upon the complex formation, but also reproduces the rotational spectroscopic characteristics much better.

Application of Clustering Algorithms to Partitioning Configuration Space in Fitting Reactive Potential Energy Surfaces.

A large number of energy points add great difficulty to construct reactive potential energy surfaces (PES). To alleviate this, exemplar-based clustering is applied to partition the configuration space into several smaller parts. The PES of each part can be constructed easily and the global PES is obtained by connecting all of the PESs of small parts. This divide and conquer strategy is first demonstrated in the fitting of PES for OH3 with Gaussian process regression (GPR) and further applied to construct PESs for CH5 and O+CH4 with artificial neural networks (NN). The accuracy of PESs is tested by fitting errors and direct comparisons with previous PESs in dynamically important regions. As for OH3 and CH5, quantum scattering calculations further validate the global accuracy of newly fitted PESs. The results suggest that partitioning the configuration space by clustering provides a simple and useful method for the construction of PESs for systems that require a large number of energy points.