A simplistic computational procedure for tunneling splittings caused by proton transfer

In this manuscript, we present an approach for computing tunneling splittings for large amplitude motions. The core of the approach is a solution of an effective one-dimensional Schrödinger equation with an effective mass and an effective potential energy surface composed of electronic and harmonic zero-point vibrational energies of small amplitude motions in the molecule. The method has been shown to work in cases of three model motions: nitrogen inversion in ammonia, single proton transfer in malonaldehyde, and double proton transfer in the formic acid dimer. In the current work, we also investigate the performance of different DFT and post-Hartree–Fock methods for prediction of the proton transfer tunneling splittings, quality of the effective Schrödinger equation parameters upon the isotopic substitution, and possibility of a complete basis set (CBS) extrapolation for the resulting tunneling splittings.

Simplistic calculation of the tunneling splittings for proton transfer in malonaldehyde and formic acid dimer using the one-dimensional Schrödinger equation

In this manuscript we present an approach for computing tunneling splittings for large amplitude motions. The core of the approach is a solution of an effective one-dimensional Schrödinger equation with an effective mass and an effective potential energy surface composed of electronic and harmonic zero-point vibrational energies of small amplitude motions in the molecule. The method has been shown to work in cases of three model motions: nitrogen inversion in ammonia, single proton transfer in malonaldehyde, and double proton transfer in the formic acid dimer. In the current work we also investigate the performance of different DFT and post-Hartree-Fock methods for prediction of the proton transfer tunneling splittings, quality of the effective Schrödinger equation parameters upon the isotopic substitution, and possibility of a complete basis set (CBS) extrapolation for the resulting tunneling splittings.

Simplistic calculation of the tunneling splittings for proton transfer in malonaldehyde and formic acid dimer using the one-dimensional Schrödinger equation

In this manuscript we present an approach for computing tunneling splittings for large amplitude motions. <br>The core of the approach is a solution of an effective one-dimensional Schrödinger equation with an effective mass and an effective potential energy surface composed of electronic and harmonic zero-point vibrational energies of small amplitude motions in the molecule.<br>The method has been shown to work in cases of three model motions: nitrogen inversion in ammonia, single proton transfer in malonaldehyde, and double proton transfer in the formic acid dimer. In the current work we also investigate the performance of different DFT and post-Hartree-Fock methods for prediction of the proton transfer tunneling splittings, quality of the effective Schrödinger equation parameters upon the isotopic substitution, and possibility of a complete basis set (CBS) extrapolation for the resulting tunneling splittings.<br>

Extrapolating DFT Towards the Complete Basis Set Limit: Lessons from the PBE Family of Functionals

<div>In this work, I derive a set of formulas for calculating extrapolation parameters based on the percentage of HF exchange and PT correlation within the functional recipe. I use a set of CBS energies from finite element calculations, calculated with PBE and related functionals, to do so.<br></div><div>The obtained extrapolation parameters perform better than previous, empirically-derived values. They are shown to be transferrable to non-PBE functionals, and the [2,3]-zeta extrapolations work well in cases with non-covalent character.<br></div>

Extrapolating DFT Towards the Complete Basis Set Limit: Lessons from the PBE Family of Functionals

<div>In this work, I derive a set of formulas for calculating extrapolation parameters based on the percentage of HF exchange and PT correlation within the functional recipe. I use a set of CBS energies from finite element calculations, calculated with PBE and related functionals, to do so.<br></div><div>The obtained extrapolation parameters perform better than previous, empirically-derived values. They are shown to be transferrable to non-PBE functionals, and the [2,3]-zeta extrapolations work well in cases with non-covalent character.<br></div>

Extrapolating DFT Towards the Complete Basis Set Limit: Lessons from the PBE Family of Functionals

<div>In this work, I derive a set of formulas for calculating extrapolation parameters based on the percentage of HF exchange and PT correlation within the functional recipe. I use a set of CBS energies from finite element calculations, calculated with PBE and related functionals, to do so.<br></div><div>The obtained extrapolation parameters perform better than previous, empirically-derived values. They are shown to be transferrable to non-PBE functionals, and the [2,3]-zeta extrapolations work well in cases with non-covalent character.<br></div>

Thionitroxyl Radical (H2NS) Isomers: Structures, Vibrational Spectroscopy, Electronic States and Photochemistry

The thionitroxyl radical (H2NS) isomers are characterized using advanced ab initio methodologies. Computations are done using standard and explicitly correlated coupled cluster, CASSCF and MRCI approaches in conjunction with large basis sets, extrapolated to the complete basis set (CBS) limit. The lowest electronic states of different isomers are mapped along the stretching coordinates, thereby confirming the existence of the four already known ground state structures, namely H2NS, H2SN, cis-HNSH and trans-HNSH. Also, it is shown that only the lowest electronic excited states are stable, whereas the upper electronic states may undergo unimolecular decomposition processes forming H + HNS/HSN or the HN + SH or N + H2S or S + NH2 fragments. These data allow an assignment of the deep blue glow observed after reactions between “active nitrogen” and H2S at the beginning of the XXth century. For stable species, a set of accurate structural and spectroscopic parameters are provided. Since small nitrogen-sulfur molecular species are of astrophysical relevance, this work may help for identifying the thionitroxyl radical isomers in astrophysical media and in the laboratory.