Accurate Numerical Computation of Rovibrational G Matrices in Molecules of Arbitrary Size.
ABSTRACT In this work we present a methodology for the accurate numerical computation of the rovibrational G matrix in any molecule.
A C++ program is developed to apply this methodology. Using polymorphism, the program can handle the output of any of the
available electronic structure codes. The objective is to compute the kinetic contribution to the rovibrational Hamiltonian
from the results of molecular structure scans, performed in heterogeneous and distributed systems such as Internet-based Grids
of computers. The numerical derivatives needed to compute the G matrix in curvilinear, internal coordinates are obtained from
an adapted Richardson extrapolation. The procedure is optimized to maximize the number of significant digits in the derivatives.
Using the program, we compute the vibrational kinetic terms for several simultaneous torsional motions in Glycolaldehyde,
Methyl formate and Ethyl methyl ether. The results show the existence of an important coupling among the torsional vibration
- SourceAvailable from: iopscience.iop.org[show abstract] [hide abstract]
ABSTRACT: Ethyl methyl ether (C2H5OCH3) has been tentatively detected in hot cores, which are quiescent high-density sources associated with regions of high-mass star formation. Up to now, the only published laboratory rotational-torsional transitions for this molecule lie at frequencies under 35 GHz. In this paper, we report the measurement and assignment of many rotational-torsional transitions of ethyl methyl ether in its vibrational-torsional ground state at frequencies through 350 GHz. A fit to experimental accuracy of over 1000 new and previously assigned transitions has allowed us to predict the frequencies of many additional transitions up to 400 GHz. The results of this work should enable astronomers to confirm the existence of ethyl methyl ether in interstellar sources.The Astrophysical Journal Supplement Series 12/2008; 144(2):277. · 16.24 Impact Factor
- [show abstract] [hide abstract]
ABSTRACT: A perturbation theory is developed for treating a system of n electrons in which the Hartree-Fock solution appears as the zero-order approximation. It is shown by this development that the first order correction for the energy and the charge density of the system is zero. The expression for the second-order correction for the energy greatly simplifies because of the special property of the zero-order solution. It is pointed out that the development of the higher approximation involves only calculations based on a definite one-body problem.
- [show abstract] [hide abstract]
ABSTRACT: The frequencies of the three large amplitude modes of dimethylamine (DMA) were analyzed using a three-dimensional (3D) model, the independent variables of which are the two torsional angles and the CNC symmetric bending angle. For this purpose, the potential energy surface and the kinetic parameters of the vibrational Hamiltonian were determined using fully optimized ab initio calculations performed at the MP2/6-311G(d,p) and MP4/6-311G(d,p) levels on 150 nuclear conformations. The positions of the two first hot bands were also calculated. The three fundamentals, 255.4, 216.9, and 409.8 cm-1, as determined with the MP4/6-311G(d,p) approximation, are in a good agreement with the experimental frequencies of 256.3, 219.4, and 383 cm-1, respectively. Torsional frequencies were compared with those obtained from a previously published two-dimensional model. The calculations confirm that the 3D model is indispensable for obtaining accurate band separations for the two different torsional modes.Journal of Physical Chemistry A - J PHYS CHEM A. 08/1998; 102(34).