When developing and assessing density functional theory methods, a finite basis set is usually employed. In most cases, however, the issue of basis set dependency is neglected. Here, we assess several basis sets and functionals. In addition, the dependency of the semiempirical fits to a given basis set for a generalised gradient approximation and a hybrid functional is investigated. The resulting functionals are then tested for other basis sets, evaluating their errors and transferability.

The Role of the Basis Set: Assessing Density Functional Theory

In a previous contribution (Mol. Phys. {\bf 103}, xxxx, 2005), we established the suitability of density functional theory (DFT) for the calculation of molecular anharmonic force fields. In the present work, we have assessed a wide variety of basis sets and exchange-correlation functionals for harmonic and fundamental frequencies, equilibrium and ground-state rotational constants, and thermodynamic functions beyond the RRHO (rigid rotor-harmonic oscillator) approximation. The fairly good performance of double-zeta plus polarization basis sets for frequencies results from an error compensation between basis set incompleteness and the intrinsic error of exchange-correlation functionals. Triple-zeta plus polarization basis sets are recommended, with an additional high-exponent $d$ function on second-row atoms. All conventional hybrid GGA functionals perform about equally well: high-exchange hybrid GGA and meta-GGA functionals designed for kinetics yield poor results, with the exception of of the very recently developed BMK functional which takes a middle position along with the HCTH/407 (second generation GGA) and TPSS (meta-GGA) functionals. MP2 performs similarly to these functionals but is inferior to hybrid GGAs such as B3LYP and B97-1.

Assessment of Various Density Functionals and Basis Sets for the Calculation of Molecular Anharmonic Force Fields

2D boron nitride material as a sensor for H2SiCl2

Semiconductor photocatalyst nanomaterials are being extensively studied for last a few decades due to their great potentials in solving energy and environmental problems on the earth by harnessing solar light....

CdS based 3D Nano/Micro-Architectures: Formation Mechanism, Tailoring of Visible Light Activities and Emerging Applications in Photocatalytic H2 Production, CO2 Reduction and Organic Pollutant Degradation

Vibrational spectroscopy represents an active frontier for the identification and characterization of molecular species in the context of astrochemistry and astrobiology. As new missions will provide more data over broader ranges and at higher resolution, especially in the infrared region, which could be complemented with new spectrometers in the future, support from laboratory experiments and theory is crucial. In particular, computational spectroscopy is playing an increasing role in deepening our understanding of the origin and nature of the observed bands in extreme conditions characterizing the ISM or some planetary atmospheres, not easily reproducible on Earth. In this connection, the best compromise between reliability, feasibility and ease of interpretation is still a matter of concern due to the interplay of several factors in determining the final spectral outcome, with larger molecular systems and non-covalent complexes further exacerbating the dichotomy between accuracy and computational cost. In this context, second-order vibrational perturbation theory (VPT2) together with density functional theory (DFT) has become particularly appealing. The well-known problem of the reliability of exchange-correlation functionals, coupled with the treatment of resonances in VPT2, represents a challenge for the determination of standardized or "black-box" protocols, despite successful examples in the literature. With the aim of getting a clear picture of the achievable accuracy and reliability of DFT-based VPT2 calculations, a multi-step study will be carried out here. Beyond the definition of the functional, the impact of the basis set and the influence of the resonance treatment in VPT2 will be analyzed. For a better understanding of the computational aspects and the results, a short summary of vibrational perturbation theory and the overall treatment of resonances for both energies and intensities will be given.The first part of the benchmark will focus on small molecules, for which very accurate experimental and theoretical data are available, to investigate electronic structure calculation methods. Beyond the reliability of energies, widely used for such systems, the issue of intensities will also be investigated in detail. The best performing electronic structure methods will then be used to treat larger molecular systems, with more complex topologies and resonance patterns.

/pdf/accuracy-and-reliability-in-the-simulation-of-vibrational-58uwgtd0zx.pdf

Accuracy and Reliability in the Simulation of Vibrational Spectra: A Comprehensive Benchmark of Energies and Intensities issuing from Generalized Vibrational Perturbation Theory to Second Order (GVPT2)

The accuracy and convergence of a series of commonly used split-valence electronic basis sets are systematically investigated for the anharmonic molecular vibrational spectroscopic calculations using the second-order perturbative corrected vibrational self-consistent field theory. A series of 18 split-valence basis sets with increasing flexibility is assessed in conjunction with MP2 and density functional theory (DFT)-based dispersion-corrected B3LYP potentials and applied to a set of molecular systems with different electronic and vibrational characteristics. The computed fundamental transitions and intensities are compared with the experimental values to assess the accuracy of different basis sets. Comparisons with high levels of Dunning basis sets, aug-cc-pVQZ along with def2-TZVPP and aug-pc-2 type basis sets, are also tested to check the convergence. A full statistical error analysis has been performed, assessing the success and failure of each basis set in terms of both accuracy and precision. The general statement "the bigger the basis, the better the results" is not strictly followed for bigger basis sets that are nearly converged to the adiabatic ab initio limit. It is found that the basis set hierarchy holds good for minimal basis sets up to polarized double-ζ basis sets. Beyond that, the improvements in comparison to experimental results or with very high end aug-cc-pVQZ and others are found rather slow. Finally, a prescription regarding the choice of a basis set for a suitable balance between accuracy and the computational time is given, which can be further used to investigate specific normal modes and large molecules as a blackbox.

Comprehensive Benchmark Results for the Accuracy of Basis Sets for Anharmonic Molecular Vibrations.

DIVA: Deep Indic Virtual Apparel Try-On

Planar defects, viz. stacking faults, grain boundaries, and twin boundaries, are observed in chemically synthesized Cd1–xMgxS quantum dots (QDs), with x ranging from 0 to 0.05 with an interval of 0...

Comprehensive Analysis of Band Gap and Nanotwinning in Cd1–xMgxS QDs

[Formula: see text]-bis (4′-tert-butylbiphenyl-4-yl)aniline) tethered zinc porphyrins, (BBA) 4 - ZnP, (BBA- Ph) 4 - ZnP, and (BBA- OEtOPh) 4 - ZnP with varied spacer distances have been synthesized and photosynthetic antenna-reaction center models were constructed via axial co-ordination with fulleropyrrolidines, C 60 Im and C 70 Im. Selective excitation of the BBA moiety in the porphyrins at 355 nm resulted in the quenching of the emission intensity of the BBA followed by the concomitant appearance of the ZnP emission at 600–640 nm indicating the occurrence of the photoinduced energy transfer from 1 BBA * to ZnP. When the zinc porphyrins are titrated with C 60 Im and C 70 Im, supramolecular complexes of the type, (BBA) 4 -ZnP:[Formula: see text]Im/[Formula: see text]Im are formed and the complex formation was monitored by UV-visible spectroscopic studies. Steady-state fluorescence studies involving the excitation of the ZnP at 550 nm displayed the diminished fluorescence intensity of the ZnP emission indicating the photoinduced electron transfer from 1 ZnP * to fullerenes. More interestingly, when the BBA moiety is excited in the supramolecular complexes, the emission of both the BBA and ZnP were decreased gradually indicating the occurrence of PEnT from 1 BBA * to ZnP followed by a sequential electron transfer from 1 ZnP * to C 60 Im or C 70 Im indicating the formation of a charge-separated state in these complexes. 

Light induced energy and electron transfer occurring in tandem in tetra (bis(4'-tert-butylbiphenyl-4-yl)aniline)-zinc(II) porphyrin-fullerene supramolecular conjugates

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Comprehensive Benchmark Results for the Accuracy of Basis Sets for Anharmonic Molecular Vibrations.

DIVA: Deep Indic Virtual Apparel Try-On

Comprehensive Analysis of Band Gap and Nanotwinning in Cd1–xMgxS QDs

Light induced energy and electron transfer occurring in tandem in tetra (bis(4'-tert-butylbiphenyl-4-yl)aniline)-zinc(II) porphyrin-fullerene supramolecular conjugates