Anharmonic force fields from analytic second derivatives: Method and application to methyl bromide

Vibrational solvatochromic frequency shift of IR probe is an effect of interaction between local electric field and IR probe in condensed phases. Despite prolonged efforts to develop empirical maps for vibrational frequency shifts and transition dipoles of IR probes, a systematic approach to ab initio calculation of vibrational solvatochromic charges and multipoles has not been developed. Here, we report on density functional theory (DFT) calculations of N-methylacetamide (NMA) frequency shifts using implicit and coarse-grained models. The solvatochromic infrared spectral shifts are estimated based on the distributed multipole analysis of electronic densities calculated for gas-phase equilibrium structure of NMA. Thus obtained distributed solvatochromic multipole parameters are used to calculate the amide I vibrational frequency shifts of NMA in water clusters that mimic the instantaneous configurations of the liquid water. Our results indicate that the spectral shifts are primarily electrostatic in nature and can be quantitatively reproduced using the proposed model with semi-quantitative accuracy when compared to the corresponding DFT results.

Section: Distributed Solvatochromic Multipoles From Cumulativementioning

confidence: 99%

Vibrational solvatochromism: Towards systematic approach to modeling solvation phenomena

Lee¹,

Cho²

2013

“…Instead, numerical differentiation of analytic first or second derivatives has commonly been used for the calculation of these quantities. 22,50,51 Furthermore, it has been common practice to evaluate anharmonic contributions at a lower level of theory than the corresponding harmonic force field, 52 which often leads to acceptable results, but is not entirely satisfying from a rigorous point of view.…”

Section: Introductionmentioning

confidence: 99%

Analytic evaluation of the dipole Hessian matrix in coupled-cluster theory

Jagau

Gauß

Ruud

2013

The general theory required for the calculation of analytic third energy derivatives at the coupledcluster level of theory is presented and connected to preceding special formulations for hyperpolarizabilities and polarizability gradients. Based on our theory, we have implemented a scheme for calculating the dipole Hessian matrix in a fully analytical manner within the coupled-cluster singles and doubles approximation. The dipole Hessian matrix is the second geometrical derivative of the dipole moment and thus a third derivative of the energy. It plays a crucial role in IR spectroscopy when taking into account anharmonic effects and is also essential for computing vibrational corrections to dipole moments. The superior accuracy of the analytic evaluation of third energy derivatives as compared to numerical differentiation schemes is demonstrated in some pilot calculations.

“…64) at the CCSD(T) level with the ANO1 basis set. These calculations are based on an established procedure, 65,66 whereby analytic second derivatives of the energy are numerically differentiated to yield the cubic and quartic constants required by VPT2. 65,66 Finally, residual deficiencies in the quantum chemical treatment of the various electronic states under study were examined at a yet higher level of theory; the coupledcluster singles, doubles, triples, and quadruples approximation (CCSDTQ).…”

Section: Computational Aspectsmentioning

confidence: 99%

“…These calculations are based on an established procedure, 65,66 whereby analytic second derivatives of the energy are numerically differentiated to yield the cubic and quartic constants required by VPT2. 65,66 Finally, residual deficiencies in the quantum chemical treatment of the various electronic states under study were examined at a yet higher level of theory; the coupledcluster singles, doubles, triples, and quadruples approximation (CCSDTQ). With the smaller atomic natural orbital basis (ANO0), both CCSDT and CCSDTQ calculations were carried out for the ground singlet and the various triplet states (the latter with an unrestricted HartreeFock reference) at their respective equilibrium geometries.…”

Section: Computational Aspectsmentioning

confidence: 99%

Ground and low-lying excited states of propadienylidene (H2C=C=C:) obtained by negative ion photoelectron spectroscopy

Stanton

Garand

Kim

et al. 2012

A joint experimental-theoretical study has been carried out on electronic states of propadienylidene (H 2 CCC), using results from negative-ion photoelectron spectroscopy. In addition to the previously A 2 and has profound effects on the spectrum. As a result, only a weak, broadened band is observed in the energy region where the origin of theB 1 B 1 state is expected. The assignments here are supported by high-level coupled-cluster calculations and spectral simulations based on a vibronic coupling Hamiltonian. A result of astrophysical interest is that the present study supports the idea that a broad absorption band found at 5450 Å by cavity ringdown spectroscopy (and coincident with a diffuse interstellar band) is carried by theB 1 B 1 state of H 2 CCC.