On quadratic bond-order decomposition within molecular orbital space

A simple method of analysing and localization of canonical molecular orbitals for particular chemical bond using the MO-resolved bond-order decompo- sition scheme is presented. An alternative definition of classical bond order orbitals is provided and links to communication theory of the chemical bond are outlined and briefly discussed. The introduced procedure of decomposition of quadratic bond orders allows one to analyse two- as well as three- center chemical bonds within the framework of the same theory

Nucleophilicity index based on atomic natural orbitals

A simple method of evaluating a semilocal (regional) nucleophilicity is introduced. The concept involves use of the natural orbitals for atomic populations to identify the most “reactive population” of electrons on particular atom in molecule. The results of test calculations considering the regioselectivity problem in electrophilic aromatic substitution to the benzene derivatives are presented and briefly discussed

Minimal set of molecule-adapted atomic orbitals from maximum overlap criterion

The criterion of maximum overlap with the canonical free-atom orbitals is used to construct a minimal set of molecule-intrinsic orthogonal atomic orbitals that resemble the most their promolecular origins. Partial atomic charges derived from population analysis within representation of such molecule-adopted atomic orbitals are examined on example of first-row hydrides and compared with charges from other methods. The maximum overlap criterion is also utilized to approximate the exact free-atom orbitals obtained from ab initio calculations in any arbitrary basis set and the influence of the resulting fitted canonical atomic orbitals on properties of molecule- adopted atomic orbitals is briefly discussed

Basis set dependence of molecular information channels and their entropic bond descriptors

Information channels from SCFMOcalculations using different basis sets and their entropic bond descriptors are compared within the orbital communication theory. In this information-theoretic (IT) treatment of communications between basis functions the overall covalency and ionicity bond components reflect the average communication noise and information flow, respectively, in the resolution level specified by the adopted set of basis functions. The basis-set dependence of the orbital conditional probabilities and their entropic descriptors of the information covalency/ionicity content is explored. Compared to theminimum set χ of the occupied atomic orbitals of the separated constituent atoms, the extended basis sets of Gaussian orbitals and/or their formal contractions generally give rise to a higher IT-covalency and lower IT-ionicity descriptors of the system chemical bonds. In the augmented set case, χaug. = (χ,ψ), containing the polarization function complement ψ of χ, the use of only χ → χ communications is advocated in a semi-quantitative chemical interpretation of the IT bond indices. The maximum-overlap criterion is used to transform the general (orthonormal) extended basis ξ to its semi-augmented form χ aug. = ξ = ( χ , ψ), in which χ ≈ χ and ψ ≈ ψ,which facilitates the near minimum basis set interpretation of bond descriptors and extraction of communications involving the polarization functions ψ. A similar transformation using the minimum information distance criterion can b

Reply to the ‘Comment on “designing potentially singlet fission materials with an anti-Kasha behaviour”’ by K. Jindal, A. Majumdar and R. Ramakrishnan, <i>Phys. Chem. Chem. Phys.</i>, 2025, <b>27</b>, DOI: 10.1039/D4CP02863E

In this reply to the preceding paper by K. Jindal, A. Majumdar, and R. Ramakrishnan, we argue that the results obtained in our original manuscript with the time-dependent density functional theory (TD-DFT) are reasonable and that they are not only in agreement with experimental results but also with reliable ab initio calculations

The electron density of delocalized bonds (EDDB) applied for quantifying aromaticity

In this study the recently developed electron density of delocalized bonds (EDDB) is used to define a new measure of aromaticity in molecular rings. The relationships between bond-length alternation, electron delocalization and diatropicity of the induced ring current are investigated for a test set of representative molecular rings by means of correlation and principal component analyses involving the most popular aromaticity descriptors based on structural, electronic, and magnetic criteria. Additionally, a qualitative comparison is made between EDDB and the magnetically induced ring-current density maps from the ipsocentric approach for a series of linear acenes. Special emphasis is given to the comparative study of the description of cyclic delocalization of electrons in a wide range of organic aromatics in terms of the kekulean multicenter index KMCI and the newly proposed EDDBk indexThe research was supported in part by the Faculty of Chemistry at Jagiellonian University (grant K/DSC/001469, DS), Foundation for Polish Science (FNP START 2015, stipend 103.2015, DS), National Science Centre, Poland (NCN SONATA, grant 2015/17/ D/ST4/00558, DS) as well as the PL-Grid Infrastructure of the Academic Computer Centre CYFRONET with the calculations performed on the cluster platform ‘‘Prometheus’’. MS thanks for the support of the Ministerio de Economa y Competitividad of Spain (Project CTQ2014-54306-P), Generalitat de Catalunya (project number 2014SGR931, Xarxa de Refere`ncia en Qumica Teo`rica i Computacional, and ICREA Academia prize), and European Fund for Regional Development (FEDER grant UNGI10-4E-801

Tuning the strength of the resonance-assisted hydrogen bond in acenes and phenacenes with two o-hydroxyaldehyde groups - The importance of topology

The fact that intramolecular resonance-assisted hydrogen bonds (RAHBs) are stronger than conventional ones is attributed to the partial delocalization of the π-electrons within the hydrogen bond (HB) motif, the so-called quasi-ring. If an aromatic ring is involved in the formation of the RAHB, previous studies have shown that there is an interplay between aromaticity and HB strength. Moreover, in 1,3-dihydroxyaryl-2-aldehydes, some of us found that the position of the quasi-ring formed by the substituents interacting through RAHB influences the strength of the H bonding, the HBs being stronger when a kinked-like structure is generated by formation of the quasi-ring. In this work, we explore this concept further by considering a set of acenes and phenacenes of different sizes with two o-hydroxyaldehyde substituents. Calculations with the CAM-B3LYP/6-311++G(d,p) + GD3B method show that for long acenes or phenacenes, once the substituent effect loses importance because quasi-rings are pulled apart far from each other, the different topologies rule the HB distances. This fact can be explained in most cases using an extended Clar’s aromatic π-sextet model. In some kinked systems, however, the justification from the Clar model has to be complemented by taking into account the repulsion between hydrogen atoms. Triphenylene-like compounds with different numbers of benzene rings have been studied, finding out a very good relationship between aromaticity of the ipso- and quasi-rings with the RAHB distances. This result confirms the importance of the communication of the π-systems of the ipso- and quasi-rings