A multireference coupled-cluster method for ground and excited states calculations of interstellar molecules

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Professor Ludwik Adamowicz of the University of Arizona is supported by an award from the Chemical Theory, Models and Computational Methods program in the Division of Chemistry. His project is based on using fundamental principles of quantum mechanics (QM) in predicting chemical and physical properties of primordial molecular systems. Some of these molecules, for example, the simplest triatomic ion H3+, has played a pivotal role in the evolution of our universe. Professor Adamowicz's QM calculations will use the most powerful present-day computers to provide results pertaining to the spectral transitions and chemical behavior of molecules relevant to experimental astrochemical/astrophysical research. The major effort in this research will go to the development of new QM computational methods whose accuracy matches or even exceeds the accuracy of present-day experimental measurements. Most of our knowledge of the astronomical world is derived from the absorption, emission and scattering of electromagnetic radiation from atoms and molecules. Astronomical observations of atomic and molecular spectra, including transition energies, intensities, and light polarization, complement both laboratory experiments and the new theoretical calculations from the Adamowicz group to develop a better understanding of stellar atmospheres and their evolutions. Professor Adamowicz will engage both science and non-science undergraduate students in the application of modern computational methods. He makes the new software developed in this project available to the broader scientific community.Professor Adamowicz and his group are developing new methods that utilize first-principles quantum mechanics to study chemical and physical properties of small and medium-size molecular systems in the gas phase. The methods are expected to elevate the predictive capability of computational quantum chemistry to a level of accuracy unattainable using present-day approaches. The first focus is on an active-space multireference coupled-cluster method that can be applied to study molecules in their ground and excited states at and away from their equilibrium structures. The second focus is on developing methods for performing molecular calculations with all-electron explicitly correlated Gaussian (ECG) functions. Methods based on the Born-Oppenheimer (BO) approximation and non-BO methods are also being developed. The ECGs are implemented in rovibrational calculations. Professor Adamowicz and his group are applying the new methods to study properties and spectra of various molecular systems such as HCO+, CH5+, H3+, HeH2+, HeH, LiHe+, BeH+, LiH2+, etc.. These are all important to the interstellar chemistry of the universe from its primordial stages to the present.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.