Prasenjit Seal

CH/π Interaction in Benzene and Substituted Derivatives with Halomethane: A Combined Density Functional and Dispersion-Corrected Density Functional Study

The present work intends to establish the efficiency of dispersion-corrected density functionals in explaining the potential energy curves of benzene-methane, benzene-fluoroform, and 1,3,5-trifluoro benzene-methane complexes. The interaction energies of all of the complexes under investigation have been evaluated using both van der Waals-corrected and normal gradient-corrected Perdew-Burke-Ernzerhof and Becke-Lee-Yang-Parr density functionals. Our analyses suggest that the potential energy curves for both benzene-methane and benzene-fluoroform complexes are in excellent agreement with highly accurate coupled cluster (CCSD(T)) results as well as high-level counterpoise-corrected MP2 results. Remarkably, the interaction energies of the benzene-fluoroform complex are fairly higher than those of the other two complexes. This is primarily attributed to the dispersion correction present in it. Finally, the overall study highlights the importance of halogen substitution in strengthening the CH/pi interactions.

Searching of potential energy curves for the benzene dimer using dispersion-corrected density functional theory.

The present work aims to establish the utility of dispersion-corrected density functional theory for potential energy curves of the benzene dimer, a problem that has received significant attention for a long time. The interaction energies of parallel-stacked, T-shaped and parallel-displaced benzene dimer configurations have been evaluated using both dispersion- and normal gradient-corrected Perdew-Burke-Ernzerhof functionals along with Dunnings augmented correlation-consistent polarized valence triple-zeta (aug-cc-pVTZ) basis functions and compared with explicit correlation methods. The potential energy curves for the parallel-stacked and parallel-displaced benzene dimers are in excellent agreement with highly accurate coupled cluster (CCSD(T)) results, while for the T-shaped benzene dimer the dispersion-corrected results show a distinct deviation, being closer in that case to the MP2 level of results. The overestimation of interaction energy in the T-shaped dimer may be attributed to the presence of a permanent dipole moment in this configuration and indicates a structural dependence of the dispersion-corrected density functional method.

Nonlinear optical switching properties in the furylfulgide aberchrome 540-dihydrobenzofuran derivative pair of photochromic materials.

Time-dependent density functional theoretical investigation has been carried out to justify the switching action of nonlinear optical properties in the furylfulgide Aberchrome 540 (FFA) and dihydrobenzofuran derivative (DHBF) photochromic pair of molecules. The effect of solvents on this switching action has also been addressed. The calculations suggest that DHBF has a higher optical coefficient compared to that of FFA. Notably, a dramatic increase in DHBF is observed in the second harmonic data, particularly in the solvent phase. The ratio of SHG tensor gradually decreases as the polarity of the solvent is decreased using a coulomb-attenuating functional irrespective of the basis sets used. An exploration of the excitation parameters suggests that high excited-state dipole moments are responsible for the observed large beta value in the case of the DHBF system relative to that of the FFA system.

Suitability of Double Hybrid Density Functionals and Their Dispersion-Corrected Counterparts in Producing the Potential Energy Curves for CO2-Rg (Rg: He, Ne, Ar and Kr) Systems

The present work aims to establish the suitability of double hybrid density functionals in explaining the potential energy curves of carbon dioxide-rare gas (CO(2)-Rg; Rg: He, Ne, Ar, and Kr) systems. The interaction energies of the most stable T-shaped configuration of all CO(2)-Rg systems have been evaluated using pure gradient-corrected functionals and double hybrid density functionals and their dispersion-corrected analogs with the use of Dunnings augmented correlation consistent polarized valence triple-zeta (aug-cc-pVTZ) basis function. The equilibrium separation distance, r, between CO(2) and Rg obtained from the potential energy curves for these CO(2)-Rg systems are then compared with the experimental as well as with some earlier theoretical non-density functional theory (non-DFT) results. Our investigation suggests that for CO(2)-Ar/Kr systems, the r values obtained using the short-range corrected double hybrid mPW2PLYP functional is in excellent agreement with the experimental distances of separation. On the other hand, the short-range corrected double hybrid B2PLYP functional reproduces the experimental r values for the CO(2)-He/Ne systems quite satisfactorily. Interestingly, for lighter CO(2)-Rg (Rg: He and Ne) complexes, the B2PLYP functional fails to explain the potential energy surface, whereas the mPW2PLYP functional satisfactorily explains the potential well depth. On the other hand, for higher Rg complexes, none of the functionals are able to produce satisfactory potential well depth. Hence, the overall investigation suggests that, although double hybrid density functionals and other density functionals are good for predicting separation distance, they fail to produce correct interaction energy values in higher CO(2)-Rg complexes.

Magnetic interactions in alkyl substituted cyclohexane diradical systems: a broken symmetry approach.

Magnetic interactions in alkyl substituted cyclohexane diradical systems have been investigated within the framework of spin flip density functional theory. The investigations suggest a ferromagnetic interaction for both the alkyl substituted cyclohexane-1,3-diyls and cyclohexane-1,4-diyls. However, in the case of cyclohexane-1,3-diyls, the ferromagnetic interaction is much stronger than its 1,4 analogue. Interestingly, it has been observed that this interaction is reduced to almost half the value from the butyl to the decyl substituted unit relative to the lower homologues up to the propyl substituted unit in cyclohexane-1,3-diyls. On the other hand, in case of alkyl substituted cyclohexane-1,4-diyls, the ferromagnetic interaction for the higher homologues, i.e., butyl to decyl substituted units, substantially reduces to almost 5-6 times the value of its lower homologue (methyl and ethyl substituted unit). In both these cyclohexane diradical systems, beyond butyl substituted unit, a saturation effect in the magnetic coupling constant (J) value is observed. The rapid decrease followed by a saturation in the singlet-triplet gap and J as well may be explained by considering positive inductive effect of the alkyl substituent.

Role of π-Conjugation in Influencing the Magnetic Interactions in Dinitrenes: A Broken-Symmetry Approach

In the present study, we investigated the magnetic interactions of some dinitrenes by employing the broken symmetry-unrestricted density functional theoretical (BS-UDFT) approach along with the use of three basis sets. The magnetic coupling parameter (J) has been calculated, and thereby the magnetic character of the molecule and the strength of magnetic interaction are explored for these molecules. The exchange coupling parameters for the corresponding unconjugated systems are also calculated to see the role of pi-conjugation. Our results suggest that a strong antiferromagnetic interaction exists in conjugated dinitrenes, and the strength of magnetic interaction decreases with increase in spacer length. For the unconjugated dinitrenes, the nature of magnetic interaction reduced appreciably and becomes weakly antiferromagnetic. The singlet-triplet energy gap for each system is also calculated. For the conjugated systems, it is observed that the singlet states are more stable than the triplet states, whereas for the unconjugated systems, the relative stability of the singlet state reduces to a considerable extent. This discrepancy of results for the conjugated and unconjugated dinitrenes can be attributed to the effect of pi-conjugation, and the results can be well explained by this effect.

Carbondioxide rare‐gas systems: Sensitivity of basis sets and double‐hybrid density functionals

This study emphasizes on the performance of six newly developed double‐hybrid density functionals (DHDF) in explaining the potential energy curves of different carbondioxide rare‐gas systems. The basis set sensitivity has also been explored with the use of three basis sets. Our results suggest that for lighter He/Ne‐CO2 complexes, proper choice of DHDF and basis set lead to results those matches exactly with earlier calculations and also with the experiment. On the other hand, for heavier Ar/Kr‐CO2 complexes although the equilibrium separation distance matches exactly with earlier observations, the interaction energy values lie far apart. The overall investigation emphasizes on the fact that one has to tune the methods and basis sets properly to achieve good and satisfactory results.