Explicitly correlated frequency-independent second-order green's function for accurate ionization energies

Area of Science:

• Computational Chemistry
• Theoretical Chemistry
• Quantum Chemistry

Background:

• Standard ab initio methods, including second-order Green's function (GF2), face slow convergence in orbital expansions.
• Accurate calculation of ionization energies (IE) is crucial for understanding molecular electronic structure.
• Polycyclic aromatic hydrocarbons (PAHs), oligothiophene, and porphyrins are important molecular systems with complex electronic properties.

Purpose of the Study:

• To introduce and apply the explicitly correlated second-order Green's function (GF2-F12) method.
• To address the slow convergence limitations of traditional GF2 calculations.
• To achieve accurate ionization energies for challenging molecular systems.

Main Methods:

• Implementation of the explicitly correlated F12 terms within the second-order Green's function (GF2) framework.
• Application of the GF2-F12 method to polycyclic aromatic hydrocarbons (PAHs), oligothiophene, and porphyrins.
• Utilizing augmented triple-zeta quality basis sets for calculations.

Main Results:

• The GF2-F12 method significantly mitigates the slow convergence problem of standard GF2.
• Accurate ionization energies (IE) were obtained, approaching the complete basis set limit.
• For PAHs, errors compared to experimental results were typically less than 0.15 eV.

Conclusions:

• GF2-F12 offers a computationally efficient and accurate approach for calculating ionization energies.
• The method provides quantitatively accurate results comparable to higher-level theoretical methods.
• GF2-F12 is a valuable tool for studying the electronic properties of complex organic molecules.