Report on the outcomes of a Short-Term Scientific Mission

Action number: CA21101

Applicant name: Dariusz Kędziera

Details of the STSM

Title: Potential energy surface for the H2Cl+ –H2 collisional system

Start and end date: 16/10/2023 to 21/10/2023

Description of the work carried out during the STSM

The internship with Prof. Francois Lique’s group in Rennes was designed to generate a highly accurate site-site potential energy surface for the astrochemically significant H2Cl+ and H2 systems. This was done using the AutoPES computational package from the K. Szalewicz group. Additionally, an interface was developed to transform the acquired site-site potential into Jacobi coordinates, which are used in collisional calculations. Preliminary results using the aug-cc-pvqz basis set produced potentials where the RMSE of the interaction energy below 0 cm-1 was approximately 240cm-1 for SAPT(DFT) and 160cm-1 for CCSD(T). During this STSM, the following tasks were carried out:

  1. The fit quality was improved by adding off-atomic sites (OAS) and optimizing their positions to achieve an RMSE of less than 10 cm-1 for interaction energies below 0cm-1. A general procedure was developed for this purpose, which can also be applied to other systems. The obtained potentials were then verified using standard CCSD(T) and CCSD(T)-F12 using various basis sets. The agreement was excellent, particularly for long and medium ranges. However, for short ranges, we found that SAPT(DFT) energies were significantly lower than CCSD(T), which manifested in shifts of the SAPT(DFT) based potential surface cuts in this region by up to 0.1 Bohr in comparison with CCSD(T) based potential. The impact of this behavior will now be examined in collisional calculations.
  2. An interface was developed to convert the site-site potential for interaction of H2Cl+ and H2 obtained from AutoPES into Jacobi coordinates for collisional calculations.
  3. Additionally, going beyond the previously proposed plan, interface allowing using CCSD(T)-F12 method with autoPES was implemented.

Obtained potentials are now ready used for collisional dynamics studies to provide reliable rate coefficients for H2Cl+ interacting with H2. This part of calculations will be performed mainly in the Rennes group.

Description of the STSM main achievements and planned follow-up activities

The primary objectives of the STSM were successfully achieved. Highly accurate potentials for the interaction of H2Cl+ with H2 were produced. Additionally, numerous interfaces for AutoPES were developed during this stay, facilitating the efficient utilization of this package for determining interaction potentials of systems that are significant in astrochemistry. Furthermore the capabilities of the AutoPES package were expanded by interfacing it with the CCSD(T)-F12 method.

The tasks completed during this STSM are in line with the objectives of the COSY Action as outlined in the MoU: the development of protocols for SAPT and supermolecular interaction energy calculations, and the assessment of SAPT and supermolecular methods. This aligns with both WG5’s objectives (astrochemical applications) and WG1’s objectives (interaction potentials using the SAPT based and CCSD(T) methods).

Work is currently underway to utilize the obtained potentials in collisional calculations. This portion of the work will primarily be conducted by the group in Rennes. Upon completion, the results are planned to be published in a journal dedicated to astrochemistry or quantum chemistry.

The successful completion of the project focused on collisional studies involving the H2Cl+-H2 system has paved the way for a more expansive and fruitful collaboration between research centers in Rennes and Toruń. By leveraging the newly developed methodology, both centers are now poised to conduct comprehensive and efficient analyses of non-reactive collisions within astrochemical frameworks. Such studies are crucial in advancing our understanding of space chemistry processes. Furthermore, this collaboration not only exemplifies the synergy between the two research entities but also significantly elevates our combined potential for producing high-quality publications. This mutual endeavour promises to contribute valuable insights to the broader scientific community, thereby reinforcing the global significance of our joint research efforts.

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