Performance of ab initio and DFT PCM methods in calculating vibrational spectra in solution: Formaldehyde in acetonitrile as a test case

doi:10.1016/j.cplett.2005.09.099

Chemical Physics Letters

Volume 416, Issues 4–6, 16 December 2005, Pages 206-211

https://doi.org/10.1016/j.cplett.2005.09.099 Get rights and content

Abstract

We report the anharmonic spectra calculated for formaldehyde in acetonitrile solution using quartic force fields obtained at different levels of theory in connection with the SCI-PCM continuum solvent model. The fair agreement observed with the experimental data and with the observed shifts relative to the gas phase shows that the CCSD(T)/cc-pVQZ/SCIPCM and the hybrid CCSD(T)/cc-pVTZ//B3LYP/6-31+G(d,p)/SCIPCM approaches can be recommended to calculate reliable vibrational spectra in solution for medium size systems.

Introduction

The present work deals with one of the most challenging issues in the calculation of reliable vibrational spectra in condensed phases, namely the contemporary account of anharmonicity and solute–solvent interactions. Effective modeling of solvent effects is not, of course, a new area of research, as the first attempts date back to the pioneering studies by Kirkwood [1] and Buckingham [2] in the middle of the last century. However, significant research efforts continue to be devoted to this subject, mainly due to the following reasons:

•
In many areas of research such as Chemistry, Biochemistry and Biophysics, most of the spectroscopic measurements are carried out in solution.
•
Thanks to new progresses in spectroscopic technology leading to more and more sophisticated experimental set-ups with fast data acquisition and processing, very detailed molecular information can be obtained from spectra of extremely high resolution [3], [4].
•
The most recent developments of hardware and software are allowing the use of very sophisticated quantum mechanical (QM) methods for systems of increasing dimensions. In particular, coupling of refined QM approaches to continuum solvent models [5], [6], [7] or to molecular mechanics (MM) and dynamics (MD) methods (the so-called QM/MM approaches) appears very promising for the prediction of reliable vibrational spectra in solution (see for example [8], [9], [10], [11], [12]).

Previous theoretical studies (MM, MD or QM) show that, although the shift associated with a vibrational band is well-translated globally [13], this is not the case for the positions of the bands. This problem has been addresses along two main directions. The first one is to use a suitable (general or solvent specific) scaling of the computed values. For example, Rivail et al. [14] have shown that dividing B3LYP/6-311G(d,p)/PCM harmonic frequencies by 1.04, it is possible to reproduce experimental values with an error lower than 10 cm⁻¹ for the stretching band (ν_CO) of a family of six compounds. This method has become very interesting in the study of protein structures, as the most important absorption there is due to the carbonyl group in the amide I. This approach was improved later by Cappelli et al. [15] by introducing a specific solvent scaling for the description of the carbonyl stretch of dialkyl ketones in several different solvents. However, although these approaches perform well for uncoupled vibrators like the ν_CO one, it is not well adapted to the study of complete infrared (IR) spectra. The second possibility is related to direct MD simulations. For example, works by Silvestrelli et al. and Gaigeot and Sprik [12], [16] have provided quite promising results in the framework of the Car-Parrinello approach.

Here, we propose, a third way to improve theoretical results by including the anharmonic effects in the theoretical model. We present, in this Letter, a complete theoretical study of the vibrational bands, including anharmonic contributions, for the system formed by formaldehyde in acetonitrile solution, which is very well characterized from an experimental point of view [13], [17].

Section snippets

Computational methods

For systems in which anharmonicity is small, it is possible to write the potential function as a Taylor expansion series limited to the fourth order. Quadratic, cubic, and quartic force constants are generally obtained either by fitting the electronic energy data calculated by QM methods for various nuclear configurations close to the optimized geometry, or by a finite difference procedure including first and second derivatives of the electronic energy with respect to the nuclear coordinates.

Results and discussion

Table 1 reports the complete quartic force constants calculated both in vacuo and in acetonitrile solution at CCSD(T)/cc-pVQZ and B3LYP/6-31+G** levels of theory. In the gas phase, the difference between the harmonic frequencies computed at CCSD(T)/cc-pVQZ and B3LYP/6-31+G** levels ranges between 0 and 38 cm⁻¹ (average value 15 cm⁻¹). The largest deviation is observed for the CO stretching mode incorrectly described at B3LYP level due to an overestimation of the corresponding bond length.

Acknowledgments

We acknowledge the Centre Informatique National de l’Enseignement Supérieur (CINES) for support of this work. We express our sincere gratitude to Prof. Alain Dargelos for helpful discussions and to Prof. Daisy Zhang for his invaluable comments on the manuscript.

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Performance of ab initio and DFT PCM methods in calculating vibrational spectra in solution: Formaldehyde in acetonitrile as a test case

Abstract

Introduction

Section snippets

Computational methods

Results and discussion

Acknowledgments

Chem. Phys. Lett.

J. Mol. Struct.: Theochem

Chem. Phys. Lett.

Chem. Phys.

Chem. Phys. Lett.

Chem. Phys. Lett.

J. Chem. Phys.

Proc. Roy. Soc. A

Biospectroscopy

Biopolymers

Chem. Rev.

Theor. Chem. Acc.

J. Comput. Chem.

J. Phys. Chem. A