Raman intensity calculations with the CNDO method. Part III: N,N-dimethylamide – water complexes

1985 ◽  
Vol 63 (7) ◽  
pp. 1365-1371 ◽  
Author(s):  
Eduard D. Schmid ◽  
Eleonore Brodbek
Keyword(s):  
Normal Modes ◽  
Basis Set ◽  
Water Model ◽  
Raman Intensity ◽  
Solvent Interactions ◽  
Molecular Systems ◽  
Scattering Coefficients ◽  
Intensity Calculations ◽  
Stretching Vibration ◽  
Raman Intensities

Absolute differential Raman scattering coefficients of hydrogen bondedN,N-dimethylformamide (DMF) – water complexes and a N,N-dimethylacetamide (DMA) – water complex are calculated with a variational method within the CNDO approximation using an extended basis set. Changes of Raman intensities caused by intermolecular interactions are modeled in our Raman intensity calculations and the calculated intensities of the amide I (C=O stretching), OCN bending, and N—(Me)2 stretching vibration of the DMF (and DMA) – water complexes are compared with the experimental absolute Raman intensities of DMF and DMA dissolved in water. The calculated Raman intensities of characteristic normal modes of DMF and DMA and their 1:2 amide – water model are in good agreement with the experimental data. The results show that it is possible to obtain qualitative information on solute – solvent interactions from Raman intensity calculations of complex molecular systems like hydrated DMF and DMA.

Halogen and solvent effects on the conformational, vibrational and electronic properties of 1,4-diformylpiperazine: A combined experimental and DFT study

2015 ◽  
Vol 14 (07) ◽  
pp. 1550050
Author(s):  
Cemal Parlak ◽  
Mahir Tursun ◽  
Chandraju Sadolalu Chidan Kumar ◽  
Duygu Bilge ◽  
Nadide Kazanci ◽  
...  
Keyword(s):  
Electronic Properties ◽  
Conformational Changes ◽  
Density Functional ◽  
Normal Modes ◽  
Basis Set ◽  
Functional Theory ◽  
Stretching Vibration ◽  
Energy Relationships ◽  
Ft Ir ◽  
Linear Solvation Energy

The molecular structure and properties of 1,4-diformylpiperazine (1,4-dfp, C6H[Formula: see text]N2O2) were investigated by Fourier transform infrared (FT-IR) spectroscopy, Raman spectroscopy and density functional theory (DFT). The Becke-3-Lee–Yang–Parr (B3LYP) functional was used with the 6-31[Formula: see text]G(d,p) basis set. Total energy distribution (TED) analysis of normal modes was performed to identify characteristic frequencies by the scaled quantum mechanical (SQM) method. Halogeno-analogs of 1,4-dfp were studied to understand the halogen effect. Computations were focused on five conformational isomers of the compounds in the gas phase and in solutions. The computed and experimental frequencies of the C[Formula: see text]O stretching vibration of 1,4-dfp were correlated with the empirical solvent parameters such as the Kirkwood–Bauer–Magat (KBM) equation, the solvent acceptor number (AN), Swain parameters and linear solvation energy relationships (LSER). The electronic properties of the compounds were also examined. The findings from the present work may be useful to understand systems involving the halogens and conformational changes analogous to the compounds investigated.

scholarly journals 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)

2021 ◽  
Vol 8 ◽  
Author(s):  
Qin Yang ◽  
Marco Mendolicchio ◽  
Vincenzo Barone ◽  
Julien Bloino
Keyword(s):  
Perturbation Theory ◽  
Electronic Structure ◽  
Density Functional ◽  
Computational Cost ◽  
Theoretical Data ◽  
Infrared Region ◽  
Second Order ◽  
Basis Set ◽  
Molecular Systems ◽  
The Impact

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 interstellar medium 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.

Ab Initio SCF Procedure with Localized Molecular Orbitals of Fragments

1975 ◽  
Vol 30 (11) ◽  
pp. 1499
Author(s):  
J. Koller ◽  
A. Ažman
Keyword(s):  
Ab Initio ◽  
Molecular Orbitals ◽  
Basis Set ◽  
Localized Orbitals ◽  
Localized Molecular Orbitals ◽  
Molecular Systems

An ab initio procedure is described with a basis set of localized orbitals of the fragments. The method was tested on three molecular systems. The results are in agreement with the results of LCAO calculations

CALCULATION OF SELECTED HIGHLY EXCITED VIBRATIONAL STATES OF POLYATOMIC MOLECULES BY THE DAVIDSON ALGORITHM

2003 ◽  
Vol 02 (04) ◽  
pp. 609-620 ◽  
Author(s):  
FABIENNE RIBEIRO ◽  
CHRISTOPHE IUNG ◽  
CLAUDE LEFORESTIER
Keyword(s):  
Energy Levels ◽  
Normal Modes ◽  
Chem Phys ◽  
Polyatomic Molecules ◽  
Zero Order ◽  
Basis Set ◽  
Vibrational States ◽  
Diagonalization Method ◽  
Davidson Algorithm ◽  
High Overtone

We described an improved version of a modified Davidson scheme previously introduced (F. Ribeiro, C. Iung and C. Leforestier, Chem. Phys. Lett.362, 199 (2002)), aimed at computing highly excited energy levels of polyatomic molecules. The key ingredient is a prediagonalization-perturbation step performed on a subspace of a curvilinear normal modes basis set (including diagonal anharmonicities). The efficiency of the method is demonstrated by computing the lowest 350 vibrational states of A′ symmetry of the HFCO molecule. Also shown is the possibility to restrict the calculation to selected energy levels, based on their zero-order description. This State Filtered Diagonalization method is illustrated on a high overtone (7ν5) of the OCF bend, and on the few energy levels (20) which have been experimentally assigned up to 5000 cm -1 of excitation energy.

scholarly journals DFT study of species derived from the narcotic antagonist naloxone

2020 ◽  
Vol 10 (2) ◽  
pp. 5096-5116
Keyword(s):  
Force Fields ◽  
Normal Modes ◽  
Tropane Alkaloids ◽  
Solvation Energy ◽  
Basis Set ◽  
Free Base ◽  
Harmonic Force ◽  
Energy Value ◽  
Vibrational Assignments ◽  
Solvation Energies

The functional hybrid B3LYP and the 6-31G* basis set have been employed to study the theoretical structures of free base, cationic and hydrochloride species of naloxone in gas phase and in aqueous solution. The SCRF methodology and the PCM method were used to optimize the species in solution while the solvation energies were computed with the universal solvation model. The harmonic force fields of three species in the two media were computed with the SQMFF methodology and the Molvib program while the complete vibrational assignments of bands observed in the experimental available ATR and Raman spectra were performed by using the harmonic force fields and the normal internal coordinates. Therefore, the expected 129, 132 and 135 vibration normal modes for the free base, cationic and hydrochloride species of naloxone, respectively are here reported. The free base of naloxone evidence the higher solvation energy value, as compared with those reported for S(-)-promethazine, R(+)-promethazine, cyclizine, morphine, cocaine, scopolamine, heroin, and tropane alkaloids. The cationic species shows a solvation energy value (-302.45 kJ/mol) closer to observed for morphine (-309.19 kJ/mol) while the value for the hydrochloride species (-122.28 kJ/mol) is near to scopolamine value (-122.74 kJ/mol). AIM analyses show ionic characteristic of N-HCl bonds in the hydrochloride species and suggest that this species in both media is as cationic one, as supported by the positive MK charges on the N5 atoms in the hydrochloride species in both media and by the absence in the ATR spectrum of band at 2405 cm-1, associated to N5-H46 stretching mode. Moreover, frontier orbitals studies evidence that the allyl chains present in the three species of naloxone diminishing the gap values increasing their reactivities, as compared with the other species containing the N-CH3 group. The f(N-H) force constants for the hydrochloride species is lower than the corresponding in solution, a result also observed for morphine (2.73 and 4.61 mdyn Å-1), cocaine (3.23 and 4.79 mdyn Å-1) and tropane (2.70 and 4.69 mdyn Å-1) alkaloids. Comparisons between experimental infrared, Raman and ultraviolet-visible spectra with the corresponding predicted show good correlations.

scholarly journals The Performance of Dunning, Jensen and Karlsruhe Basis Sets on Computing Relative Energies and Geometries

2019 ◽  
Author(s):  
Karl Kirschner ◽  
Dirk Reith ◽  
Wolfgang Heiden
Keyword(s):  
Systematic Study ◽  
Transition States ◽  
Water Dimer ◽  
Basis Set ◽  
Basis Sets ◽  
Quantum Mechanical ◽  
Mechanical Modeling ◽  
Molecular Systems ◽  
Speed And Accuracy ◽  
Do So

<div>In an effort to assist researchers in choosing basis sets for quantum mechanical modeling of molecules (i.e. balancing calculation cost versus desired accuracy), we present a systematic study on the accuracy of computed conformational relative energies and their geometries in comparison to MP2/CBS and MP2/AV5Z data, respectively. In order to do so, we introduce a new nomenclature to unambiguously indicate how a CBS extrapolation was computed. Nineteen minima and transition states of buta-1,3-diene, propan-2-ol and the water dimer were optimized using forty-five different basis sets. Specifically, this includes one Pople (i.e. 6-31G(d)), eight Dunning (i.e. VXZ and AVXZ, X=2-5), twenty-five Jensen (i.e. pc-n, pcseg-n, aug-pcseg-n, pcSseg-n and aug-pcSseg-n, n=0-4) and nine Karlsruhe (e.g. def2-SV(P), def2-QZVPPD) basis sets. The molecules were chosen to represent both common and electronically diverse molecular systems. In comparison to MP2/CBS relative energies computed using the largest Jensen basis sets (i.e. n=2,3,4), the use of smaller sizes (n=0,1,2 and n=1,2,3) provides results that are within 0.11--0.24 and 0.09-0.16 kcal/mol. To practically guide researchers in their basis set choice, an equation is introduced that ranks basis sets based on a user-defined balance between their accuracy and calculation cost. Furthermore, we explain why the aug-pcseg-2, def2-TZVPPD and def2-TZVP basis sets are very suitable choices to balance speed and accuracy.</div>

scholarly journals The Performance of Dunning, Jensen and Karlsruhe Basis Sets on Computing Relative Energies and Geometries

2019 ◽  
Author(s):  
Karl Kirschner ◽  
Dirk Reith ◽  
Wolfgang Heiden
Keyword(s):  
Systematic Study ◽  
Transition States ◽  
Water Dimer ◽  
Basis Set ◽  
Basis Sets ◽  
Quantum Mechanical ◽  
Mechanical Modeling ◽  
Molecular Systems ◽  
Speed And Accuracy ◽  
Do So

<div>In an effort to assist researchers in choosing basis sets for quantum mechanical modeling of molecules (i.e. balancing calculation cost versus desired accuracy), we present a systematic study on the accuracy of computed conformational relative energies and their geometries in comparison to MP2/CBS and MP2/AV5Z data, respectively. In order to do so, we introduce a new nomenclature to unambiguously indicate how a CBS extrapolation was computed. Nineteen minima and transition states of buta-1,3-diene, propan-2-ol and the water dimer were optimized using forty-five different basis sets. Specifically, this includes one Pople (i.e. 6-31G(d)), eight Dunning (i.e. VXZ and AVXZ, X=2-5), twenty-five Jensen (i.e. pc-n, pcseg-n, aug-pcseg-n, pcSseg-n and aug-pcSseg-n, n=0-4) and nine Karlsruhe (e.g. def2-SV(P), def2-QZVPPD) basis sets. The molecules were chosen to represent both common and electronically diverse molecular systems. In comparison to MP2/CBS relative energies computed using the largest Jensen basis sets (i.e. n=2,3,4), the use of smaller sizes (n=0,1,2 and n=1,2,3) provides results that are within 0.11--0.24 and 0.09-0.16 kcal/mol. To practically guide researchers in their basis set choice, an equation is introduced that ranks basis sets based on a user-defined balance between their accuracy and calculation cost. Furthermore, we explain why the aug-pcseg-2, def2-TZVPPD and def2-TZVP basis sets are very suitable choices to balance speed and accuracy.</div>

Sign in / Sign up

Export Citation Format

Share Document