On the stability of Be3: a benchmark complete active space self-consistent field + averaged quadratic coupled cluster...

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Theoretical Chemistry

Background:

• Understanding the electronic structure and bonding of small atomic clusters like the beryllium trimer (Be3) is crucial in materials science and quantum chemistry.
• Previous theoretical studies have provided benchmark values, but further high-level computational investigations are needed for precise characterization.

Purpose of the Study:

• To accurately determine the optimized geometries and binding energies of the linear and triangular isomers of the beryllium trimer.
• To establish new benchmark computational data for the Be3 system using advanced quantum chemical methods and large basis sets.

Main Methods:

• Employed benchmark multireference averaged quadratic coupled cluster (AQCC) calculations with extensive complete active space self-consistent field (CASSCF) references.
• Utilized large basis sets, including cc-pV5Z for geometry optimization and aug-cc-pV5Z for binding energy calculations, with counterpoise correction.
• Analyzed bonding patterns using the electron pair localization function (EPLF) at the CASSCF(12,15) level.

Main Results:

• Calculated binding energies of 27.3 kcal/mol for the equilateral isomer and 16.3 kcal/mol for the linear isomer.
• Determined equilibrium Be-Be distances of 4.101 a.u. (equilateral) and 4.088 a.u. (linear), which are shorter than previous benchmark values.
• Demonstrated the significant role of 2p orbitals in the molecular plane for the bonding in the equilateral Be3 isomer.

Conclusions:

• The obtained results represent high-accuracy reference data for the beryllium trimer (Be3) due to the advanced methodology and large basis sets employed.
• The study provides a detailed understanding of the bonding characteristics, highlighting the importance of specific atomic orbitals in cluster stability.