Hydrogen-designed spin-states of 2D silicon carbide and graphene nanostructures.

Identifying and manipulating spin in two-dimensional materials is of great interest in advancing quantum information and sensing technologies, as well as in the development of spintronic devices. Here, we investigate the influence of hydrogen adsorption on the electronic and magnetic properties of graphene-like triangulenes. We have constructed triangulenes from SiC monolayers, which have been successfully synthesized very recently, extending our investigation to include graphene triangulenes.

Ortho-Para Conversion for H + H Collision in Low Temperature: A Fully Close-Coupled Time-Dependent Wave Packet Study.

The collision-induced rate coefficients of ortho-para conversion for the H + H reaction provide accurate information to probe the lifetime of cold environments in interstellar media. Rotationally resolved reaction probabilities are calculated at the low collision energy regime (0 < ≤ 0.3 eV) by employing the coupled three-dimensional (3D) time-dependent wave packet (TDWP) formalism in hyperspherical coordinates on a recently constructed ab initio ground adiabatic potential energy surface of H [ , , 204306] for the process H + H ( = 0, = 0-5) → H + H (' = 0, ').

Optimized infrared spectrum of mixtures.

Using density functional theory at D3-B3LYP/aug-cc-pVDZ level combined with the conductor-like polarizable continuum model (CPCM) solvent model, a study of the IR spectrum of :HCN mixtures is reported. The CPCM solvent effect notably enhances the accuracy of the IR spectra compared to gas-phase calculations, while the dielectric constant value has minimum impact on the final spectrum. An optimized methodology is suggested that effectively minimizes the root mean square deviation between theoretical and experimental data.

On the rearrangement and dissociation mechanism of SiH4+ in its triply-degenerate ground state.

An ab initio molecular orbital study has been performed to explore the structural rearrangement and dissociation of SiH4+ radical cation at the X̃2T2 ground electronic state. All stationary points located on the lowest adiabatic sheet of Jahn-Teller (JT) split X̃2T2 state are fully optimized and characterized by performing harmonic vibrational frequency calculations. The structural rearrangement is predicted to start with JT distortions involving the doubly-degenerate (e) and triply-degenerate (t2) modes.

Accurate diabatization based on combined-hyperbolic-inverse-power-representation: 1,2 2A' states of BeH2.

A diabatic potential energy matrix (DPEM) for the two lowest states of BeH2+ has been constructed using the combined-hyperbolic-inverse-power-representation (CHIPR) method. By imposing symmetry constraints on the coefficients of polynomials, the complete nuclear permutation inversion symmetry is correctly preserved in the CHIPR functional form. The symmetrized CHIPR functional form is then used in the diabatization by ansatz procedure.

Correction: Quantum and semiclassical studies of nonadiabatic electronic transitions between N(S) and N(D) by collisions with N.

Correction for 'Quantum and semiclassical studies of nonadiabatic electronic transitions between N(S) and N(D) by collisions with N' by Dandan Lu , , 2023, , 15656-15665, https://doi.org/10.1039/D3CP01429K.

High-accuracy DMBE potential energy surface for CNO(A''4) and the rate coefficients for the C + NO reaction in the A'2, A''2, and A''4 states.

An accurate potential energy surface (PES) for the lowest lying A''4 state of the CNO system is presented based on explicitly correlated multi-reference configuration interaction calculations with quadruple zeta basis set (MRCI-F12/cc-pVQZ-F12). The ab initio energies are fitted using the double many-body expansion method, thus incorporating long-range energy terms that can accurately describe the electrostatic and dispersion interactions with physically motivated decaying functions. Together with the previously fitted lowest A'2 and A''2 states using the same theoretical framework, this constitutes a new set of PESs that are suitable to predict rate coefficients for all atom-diatom reactions of the CNO system.

Quantum and semiclassical studies of nonadiabatic electronic transitions between N(S) and N(D) by collisions with N.

The dynamics and kinetics of spin-forbidden transitions between N(D) and N(S) collisions with N molecules are investigated using a quantum wave packet (WP) method and the semi-classical coherent switches with decay of mixing (CSDM) method. These electronic transition processes are competing with exchange reaction channels on both the doublet and quartet potential energy surfaces. The WP and CSDM quenching rate coefficients are found in reasonable agreement with each other, and both reproduce the previous theoretical results.

Carbon-[]Triangulenes and Sila-[]Triangulenes: Which Are Planar?

Using our recently suggested concept of a quasi-molecule ("tile") and, in the case of the planarity here at stake, its generalization to larger than tetratomics, we explain why carbon []triangulenes tend to be planar, while hybrids, where just a few or even all - or -type carbon atoms are silicon-substituted (sila-[]triangulenes), tend to be planar/nonplanar when compared with the unsubstituted carbon-[]triangulenes. Because other spin states of the parent carbon- and sila-[]triangulenes tend to correlate with the same tiles, it is conjectured that no structural changes are expected to depend on their spin state. Other polycyclic and sila-compounds are also discussed.

Scale-free-modeling (harmonic) vibrational frequencies: Assessing accuracy and cost-effectiveness by CBS extrapolation.

Empirical scaling of calculated vibrational harmonic frequencies is a popular approach used in the field of molecular sciences. A nonempirical scheme that aims at reducing their basis set error is suggested here. Nearly as cost-effective as the scaled Kohn-Sham density functional theory (KS DFT), it consists of splitting the frequencies into Hartree-Fock and electron correlation contributions, followed by their extrapolation to the complete basis set (CBS) limit.

Reconciling spectroscopy with dynamics in global potential energy surfaces: The case of the astrophysically relevant SiC.

SiC is a fascinating molecule due to its unusual bonding and astrophysical importance. In this work, we report the first global potential energy surface (PES) for ground-state SiC using the combined-hyperbolic-inverse-power-representation method and accurate ab initio energies. The calibration grid data are obtained via a general dual-level protocol developed afresh herein that entails both coupled-cluster and multi-reference configuration interaction energies jointly extrapolated to the complete basis set limit.

Quasiclassical Trajectory Study of the Si + SH Reaction on an Accurate Double Many-Body Expansion Potential Energy Surface.

An accurate potential energy surface (PES) for the HSiS system based on MRCI+ calculations extrapolated to the complete basis set limit is presented. Modeled with the double many-body expansion (DMBE) method, the PES provides an accurate description of the long-range interactions, including electrostatic and dispersion terms decaying as , , , , that are predicted from dipole moments, quadrupole moments, and dipolar polarizabilities, which are also calculated at the MRCI+ level. The novel PES is then used in quasiclassical trajectory calculations to predict the rate coefficients of the Si + SH → SiS + H reaction, which has been shown to be a major source of the SiS in certain regions of the interstellar medium.

From six to eight Π-electron bare rings of group-XIV elements and beyond: can planarity be deciphered from the "quasi-molecules" they embed?

molecular orbital theory is used to study the structures of six and eight π-electron bare rings of group-XIV elements, and even larger []annulenes up to CH, including some of their mono-, di-, tri-, and tetra-anions. While some of the above rings are planar, others are nonplanar. A much spotlighted case is cyclo-octatetraene (CH), which is predicted to be nonplanar together with its heavier group-XIV analogues SiH and GeH, with the solely planar members of its family having the stoichiometric formulas CSiH and CGeH.

Optimized Structural Data at the Complete Basis Set Limit via Successive Quadratic Minimizations.

Two variants of a successive quadratic minimization method (SQM and c-SQM) are suggested to calculate the structural properties of molecular systems at the complete basis set (CBS) limit. When applied to H, HO, CHO, SH, and SO, they revealed CBS/(, ) structural parameters that significantly surpass the raw ones calculated at the basis set level. Such a performance has also been verified for the intricate case of the water dimer.

Dynamical calculations of O(P) + OH(Π) reaction on the CHIPR potential energy surface using the fully coupled time-dependent wave-packet approach in hyperspherical coordinates.

We have carried out quantum dynamics calculations for the O + OH → H + O reaction on the CHIPR [A. J. C.

Quantum and Classical Dynamics of the N(D) + N Reaction on Its Ground Doublet State N(1A″) Potential Energy Surface.

The initial state-selected dynamics of the N(D) + N(X) → N(X) + N(D) exchange reaction on its electronic ground doublet state N(1A″) potential energy surface (PES) has been studied here by time-dependent quantum mechanics (TDQM) and quasi-classical trajectory (QCT) methods. Dynamical attributes such as total reaction probabilities, state-selected integral cross sections, and initial state-selected rate constants have been calculated. The presence of metastable quasi-bound complexes in the collision process is confirmed by substantial oscillatory structures in the reaction probability curves.

Canonical and explicitly-correlated coupled cluster correlation energies of sub-kJ mol accuracy cost-effective hybrid-post-CBS extrapolation.

Cost-effectiveness and accuracy are two basic pillars in electronic structure calculations. While cost-effectiveness enhances applicability, high accuracy is sustained when employing advanced computational tools. With the gold standard method of ab initio quantum chemistry at the focal point, canonical CCSD(T) and modern explicitly correlated CCSD(T)-F12 calculations are employed hand in hand to develop accurate hybrid post-CBS extrapolation schemes, which are validated using popular training sets involving a total of 130 molecules.

Post-complete-basis-set extrapolation of conventional and explicitly correlated coupled-cluster energies: can the convergence to the CBS limit be diagnosed?

We assess benchmark correlation energies for 130 systems in test sets A24 and TS-106 both with the canonical CCSD(T) and explicitly correlated CCSD(T)-F12 methods. Aiming at enhanced accuracy, the calculated raw energies from both sets are CBS extrapolated to the complete basis set (CBS) limit and subsequently post-CBS extrapolated. Attention is focused at total energies, since their accuracy reflects on that of the interaction energies.

Accurate DMBE potential-energy surface for CNO(A″) and rate coefficients in C(P)+NO collisions.

A realistic double many-body expansion potential energy surface (PES) is developed for the A″ state of the carbon-nitrogen-oxygen (CNO) system based on MRCI-F12/cc-pVQZ-F12 ab initio energies. The new PES reproduces the fitted points with chemical accuracy (root mean square deviation up to 0.043 eV) and explicitly incorporates long range energy terms that can accurately describe the electrostatic and dispersion interactions.

Accurate Potential Energy Surface for Quartet State HN and Interplay of N() + NH(Σ) versus H + N(Σ) Reactions.

A global potential energy surface for the lowest quartet state of HN is reported for the first time from accurate multireference ab initio calculations extrapolated to the complete basis set limit using the double many-body expansion method. All its stationary points are characterized, with the lowest quartet of HN predicted to have a bent global minimum 36 kcal mol below the N() + NH(Σ) asymptote, from which it is barrierlessly achievable. The entire set of calculated ab initio points has been fitted for energies up to 1000 kcal mol above the global minimum with an RMSD of 0.

Role of Augmented Basis Sets and Quest for ab Initio Performance/Cost Alternative to Kohn-Sham Density Functional Theory.

Following a previous work, we have assessed the feasibility of MP2/CBS(, ) as an alternative to state-of-the-art density functionals. The effect of using augmented basis sets is here tested on the 76 barrier heights and 10 isomerization reactions previously utilized. Moreover, calculations for 20 sets of the GMTKN24 database for thermochemistry, kinetics, and noncovalent interactions have been performed.

A global CHIPR potential energy surface for ground-state CH and exploratory dynamics studies of reaction C + CH → C + H.

A full-dimensional global potential-energy surface (PES) is first reported for ground-state doublet CH using the combined-hyperbolic-inverse-power-representation (CHIPR) method and accurate ab initio energies extrapolated to the complete basis set limit. The PES is based on a many-body expansion-type development where the two-body and three-body energy terms are from our previously reported analytic potentials for CH(A') and C(A',A'), while the effective four-body one is calibrated using an extension of the CHIPR formalism for tetratomics. The final form is shown to accurately reproduce all known stationary structures of the PES, some of which are unreported thus far, and their interconversion pathways.

Fully coupled (J > 0) time-dependent wave-packet calculations using hyperspherical coordinates for the H + O reaction on the CHIPR potential energy surface.

Quantum dynamics of the H + O2→ O + OH reaction has been extensively studied on the adiabatic ground state of CHIPR [A. J. C.

Quasiclassical Study of the C(P) + NO(XΠ) and O(P) + CN(XΣ) Collisional Processes on an Accurate DMBE Potential Energy Surface.

The predicted rate constants for C + NO and O + CN collisions in three potential energy surfaces (PESs) for the A' state of the CNO molecule are compared using quasiclassical trajectories. Different temperature dependencies are obtained for the C + NO reaction, which are explained in terms of the long-range properties of the PESs. Recommended values and mechanistic details are also reported.

Accurate CHIPR Potential Energy Surface for the Lowest Triplet State of C.

We report the first global ab initio-based potential energy surface (PES) for ground-state triplet C(A') based on accurate energies extrapolated to the complete basis set (CBS) limit, and using the combined-hyperbolic-inverse-power-representation method for the analytical modeling. By relying on a cost-effective CBS(,) protocol, we ensure that the final form reproduces all topographical features of the PES, including its cyclic-linear isomerization barrier, with CBS(5,6)-quality. To partially account for the incompleteness of the -electron basis and other minor effects, the available accurate experimental data on the relevant diatomics were used to obtain direct-fit curves that replace the theoretical ones in the many-body expansion.