Quantum Chemical Calculation of Molecules in Magnetic Field

Abstract: This review presents a concise, yet comprehensive discussion on the evolution of theoretical methods employed to determine the ground and excited states of molecules in weak and strong magnetic fields. The weak-field cases have been studied previously in the context of NMR, where the shielding tensor was determined by correcting the Diamagnetic Shielding operator up to the second order. However, the magnetic fields due to the Neutron Stars are extremely high and cannot be treated perturbatively. Thus, in the interest of the astrophysical and astrochemical community, this review aims to elaborate on the computational advancements in quantum mechanics from Hartree-Fock (HF) to Density Functional Theory (DFT), in the context of molecules in a high (and ultrahigh) magnetic field. It is found that the mean-field approximation of electron-electron correlation, as in the case of Hartree-Fock Theory, yields inaccurate results. On the contrary, CCSD and DFT are found to overcome these challenges. However, treating eletron-electron correlations in DFT can be challenging for heavier ions as transition metals. To circumvent this, we propose the use of DFT/CCSD along with effective Hamiltonian methods, which are likely to offer physical insights with reasonable accuracy.