Ab initio many-body perturbation-theoretic study of small potassium clusters

2D phosphorus carbide as promising anode materials for Na/K-ion batteries from first-principles study

First-principles calculations based on density functional theory were used to investigate the electrochemical performance of monolayer γ-PC for Na- and K-ion batteries. Molecular dynamics simulations indicate that the monolayer γ-PC have the thermal and dynamic stability. A substantial charge transfer from the Na/K atoms to the γ-PC sheet enhances the electrical conductivity of γ-PC. The results show that the adsorption energies of Na and K are 1.53 eV and 2.04 eV, respectively, which are much higher than Na/K bulk cohesive energy and sufficiently ensure stability and safety. Additionally, the low diffusion barriers on γ-PC monolayer are 0.034 eV for Na and 0.027 eV for K, indicating excellent rate performance. The γ-PC sheet has a high theoretical capacity for both Na (519.9 mAh/g) and K (326.6 mAh/g) ion batteries, which can satisfy the requirement of energy storage devices to anode materials. Our results strongly suggest that 2D γ-PC monolayer is an exceedingly promising anode material for both NIBs and KIBs with high adsorption energies, high capacity, and low diffusion barriers.

Relativistic state-specific multireference perturbation theory incorporating improved virtual orbitals: Application to the ground state single-bond dissociation

Using four-component (4c) relativistic spinors, we present a computationally economical relativistic ab initio method for molecular systems employing our recently proposed second-order state-specific multireference perturbation theory (SSMRPT) incorporating the improved virtual orbital-complete active space configuration interaction (IVO-CASCI) reference wavefunction. The resulting method, 4c-IVO-SSMRPT [calculate one state at a time] is tested in pilot calculations on the homonuclear dimers including Li(2), Na(2), K(2), Rb(2), F(2), Cl(2), and Br(2) through the computations of the ground state potential energy curves (PECs). As SSMRPT curbs intruder effects, 4c-IVO-SSMRPT is numerically stable. To our knowledge, the SSMRPT in the 4c relativistic framework has not been explored in the past. Selective spectroscopic constants that are closely related to the correct shape and accuracy of the energy surfaces have been extracted from the computed PECs. For the halogen molecules, a relativistic destabilization of the bond has been found. Relativistic and electron correlation effects need to be incorporated to get reliable estimates. Our results are in good accordance with reference theoretical and experimental data which manifests the computational accuracy and efficiency of the new 4c-IVO-SSMRPT method. The method opens for an improved description of MR systems containing heavy elements. The inexpensiveness of IVO-CASCI makes 4c-IVO-SSMRPT method promising for studies on large systems of heavy elements.