A new ab initio ground-state dipole moment surface for the water molecule (original) (raw)
Related papers
The Journal of Chemical Physics, 1997
We report on the determination of a high quality ab initio potential energy surface ͑PES͒ and dipole moment function for water. This PES is empirically adjusted to improve the agreement between the computed line positions and those from the HITRAN 92 data base with Jр5 for H 2 16 O. The changes in the PES are small, nonetheless including an estimate of core ͑oxygen 1s) electron correlation greatly improves the agreement with the experiment. Using this adjusted PES, we can match 30 092 of the 30 117 transitions in the HITRAN 96 data base for H 2 16 O with theoretical lines. The 10, 25, 50, 75, and 90 percentiles of the difference between the calculated and tabulated line positions are Ϫ0.11, Ϫ0.04, Ϫ0.01, 0.02, and 0.07 cm Ϫ1. Nonadiabatic effects are not explicitly included. About 3% of the tabulated line positions appear to be incorrect. Similar agreement using this adjusted PES is obtained for the 17 O and 18 O isotopes. For HD 16 O, the agreement is not as good, with a root-mean-square error of 0.25 cm Ϫ1 for lines with Jр5. This error is reduced to 0.02 cm Ϫ1 by including a small asymmetric correction to the PES, which is parameterized by simultaneously fitting to HD 16 O and D 2 16 O data. Scaling this correction by mass factors yields good results for T 2 O and HTO. The intensities summed over vibrational bands are usually in good agreement between the calculations and the tabulated results, but individual line strengths can differ greatly. A high-temperature list consisting of 307 721 352 lines is generated for H 2 16 O using our PES and dipole moment function.
Chemical Physics, 1983
The dipole-moment derivatives and infrared-absorption intensities of the water dimer including scveml det~terxed 3pscis.s have been calculated using sb initio SCF techniques. The resuhs xs compsrrd \\ith ths :malogous qtuntirirrs for monomeric w;lter. In addition to the highly enhanced intensity of the immmolsculnr OH zmxch mew inrem~olaxdar modes that oc'cur in the 90400 cm-' region are also found to be very intense. An electrostatic model for the w:tter dimsr ha been explored with I view to devrtoping a possible scheme for the cltlculntion of infrared intensities of Ixger clusters. AS ;L rsa~lt of the significrtnt exchange and charge-transfer effects such a model is found to hs unrsliablr in dacrihing thi: drpok-mamat derivatives that directly involve the hydrogen bond.
High Level ab Initio Quantum Mechanical Predictions of Infrared Intensities
The Journal of Physical Chemistry A, 2002
Vibrational intensities associated with the infrared spectra of H 2 O, C 2 H 2 , HCN, H 2 CO, CH 4 , and SiH 4 were theoretically predicted by applying ab initio quantum mechanical methods at seven different levels of theory. The self-consistent field, second-order Møller-Plesset perturbation method, configuration interaction with single and double excitations, double excitations coupled-cluster, quadratic configuration interaction including single and double excitations (QCISD), coupled-cluster with single and double excitations (CCSD), and CCSD with perturbative triple excitations [CCSD(T)] levels of theory were applied. The atomic orbital basis sets employed included frozen-core double-(DZ), triple-(TZ), DZ plus single polarization (DZP), TZ plus double polarization (TZ2P), TZ plus triple polarization (TZ3P), TZ2P augmented with one set of higher angular momentum functions [TZ2P(f,d)], TZ2P(f,d) with one set of diffuse functions [TZ2P(f,d)+diff], TZ3P augmented with two sets of higher angular momentum functions [TZ3P(2f,2d)], [TZ3P(2f,2d)] with two sets of diffuse functions [TZ3P(2f,2d)+2diff], split valence plus polarization [6-311G(d,p) and 6-311G(3d,3p)], split valence with added polarization and diffuse functions [6-311++G(d,p) and 6-311++G(3d,3p)], Dunning's correlation consistent polarized valence [cc-pVXZ (X ) 2-5)] basis sets, as well as augmented correlation consistent polarized valence [aug-cc-pVXZ (X ) 2-5)] basis sets. The theoretical infrared intensities predicted at the different levels of theory for the studied molecules were compared with available experimental data.
Possibilities and limitations of ab initio calculation of vibrational spectra
Journal of Molecular Structure, 1995
Since the first systematic quantum mechanical calculations of force constants of polyatomic molecules acceptable by modem standards [1-5], ab initio calculations of vibrational spectra have become one of the most successful applications of electronic structure theory. Calculations on medium-sized organic molecules are routine now, due to unprecedented development in computer hardware and quantum chemical software. The driving force of this is computer hardware technology. Some modem workstations are delivering close to 200 Mflops/s, outperforming the supercomputers of the eighties at dramatically lower prices. The new theoretical techniques open the possibilities of qualitatively new projects, in particular parametrization of empirical force fields based on accurate ab initio results. The main shortcoming of vibrational spectroscopy as a practical structural tool is the lack of a direct spectra-structure relation. Without elaborate calculations it is not possible in general to predict the vibrational spectrum of an unknown substance with sufficient accuracy to establish its identity or conformation. (The more difficult inverse problem, i.e. the direct deduction of the structure from the spectra is much more difficult. Fortunately, this problem rarely arises, as in most practical applications the approximate identity of the substance is known.) Traditional empirical force fields perform admirably for geometries but are not accurate enough for quadratic force fields. An example is the recent MM3 force field [6] which places the B2u CC stretching fundamental of benzene (v14) at 1657 cm-1 instead of the correct assignment of 1309 cm-1; several other band are in error by more than 100 cm-1. This is to be expected, as the empirical determination of force constants suffers from the well-known problems of insufficient data and uncertain assignment. Empirical force fields, parametrized for narrow classes of compounds and employing ample spectroscopic data as input [7-9] perform much better but are too limited in scope. Some of the most recent empirical force fields, such as CFF91 of Biosym, Inc. [10] and the Merck Force Field [11] improve on this situation by using ab initio quadratic force constants as inputs, and a more general form of the potential
International Journal of Quantum Chemistry, 1998
The development of effective theoretical approaches for analytic evaluation of first, second, and third derivatives of molecular properties, in particular energy, dipole moment, and polarizability, has contributed to increased accuracy of ab initio methods in predicting vibrational spectral parameters. It has become possible to devise and test theoretical approaches for analysis of vibrational intensities using consistent and reliable results from high-level ab initio calculations. There is a second Ž . important side of the application of ab initio molecular orbital MO calculations to the study of vibrational intensities. As for many other physical and chemical phenomena, the quantum mechanical studies provide essential information about the fine mechanisms and factors determining the observed physical quantities, in our case the intensities in infrared and Raman spectra of molecules. On this basis, new theoretical formulations for infrared and Raman intensities were recently developed. Infrared intensities are transformed into quantities termed effective bond charges that are derived from dipole moment derivatives with respect to atomic Cartesian coordinates. Raman intensities are reduced to effective induced bond charges following an analogous approach. In the present work we review the relation between advances in analytic derivative ab initio quantum mechanical calculations and the development of methods for analysis and interpretation of experimental or ab initio dipole and polarizability derivatives. Brief presentation of the effective bond charge and effective induced bond charge formulations is given.
Angewandte Chemie International Edition, 2019
Using the helium nanodroplet isolation setup at the ultrabright free-electron laser source FELIX in Nijmegen (BoHeNDI@FELIX), the intermolecular modes of water dimer in the frequency region from 70 to 550 cm À1 were recorded. Observed bands were assigned to donor torsion, acceptor wag, acceptor twist, intermolecular stretch, donor torsion overtone, and in-plane and out-of-plane librational modes. This experimental data set provides a sensitive test for state-of-the-art water potentials and dipole moment surfaces. Theoretical calculations of the IR spectrum are presented using high-level quantum and approximate quasiclassical molecular dynamics approaches. These calculations use the full-dimensional ab initio WHHB potential and dipole moment surfaces. Based on the experimental data, a considerable increase of the acceptor switch and a bifurcation tunneling splitting in the librational mode is deduced, which is a consequence of the effective decrease in the tunneling barrier.
Spectroscopy from first principles: a breakthrough in water line assignments
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 1999
Variational calculations of the spectrum of both hot and room temperature water vapor have led to a major increase in the number and scope of observed vibration -rotation transitions that have full quantum number assignments. The calculations are performed using high accuracy ab initio potential energy surfaces. As demonstrated, it is also necessary to consider corrections due to adiabatic effects, non-adiabatic effects and the relativistic motions of the electrons. The result of this work has been to double the number and energy range of the measured energy levels for water. and (060) states are presented here. Analysis of these levels and the associated transitions shows unanticipated features, including rotational difference bands, and an absence of clustering. The prospects of observing quantum monodromy in the spectrum of water are discussed.