Search results for "Equilibrium geometry"

AM1 prediction of the equilibrium geometry of Si60

1993

Abstract AM1 calculations have been carried out to determine the equilibrium geometry of Si 60 . The predicted I h geometry shows that bonds may be clearly identified as single (2.297 A) or aromatic (2.092 A). Several analogies and differences between Si 60 and C 60 are pointed out. Especially remarkable is the bigger size of the Si 60 cluster, which is predicted to have a radius 2 A larger than that of the C 60 cluster. Results are compared to other levels of theory.

Analytic second derivatives for the spin-free exact two-component theory

2011

The formulation and implementation of the spin-free (SF) exact two-component (X2c) theory at the one-electron level (SFX2c-1e) is extended in the present work to the analytic evaluation of second derivatives of the energy. In the X2c-1e scheme, the four-component one-electron Dirac Hamiltonian is block diagonalized in its matrix representation and the resulting "electrons-only" two-component Hamiltonian is then used together with untransformed two-electron interactions. The derivatives of the two-component Hamiltonian can thus be obtained by means of simple manipulations of the parent four-component Hamiltonian integrals and derivative integrals. The SF version of X2c-1e can furthermore exp…

Equilibrium structure of LiCCH

2000

The equilibrium structure of propadienylidene

1999

Abstract A coupled-cluster study of the equilibrium geometry of propadienylidene (C3H2) is presented. Deviations between a recently reported experimental re structure and those computed at the CCSD(T)/cc-pVQZ and CCSD(T)/cc-pCVQZ levels are larger than expected. A closer analysis reveals that this discrepancy is due to inaccuracies in the cubic force field that was used to correct the measured rotational constants for vibrational effects. A satisfactory agreement between theory and experiment is obtained if the vibrational effects on the rotational constants are computed from harmonic and cubic force fields determined at either the CCSD(T)/cc-pVTZ and CCSD(T)/cc-pCVTZ levels. Revised values…

Exploration of the Potential Energy Landscape of Aniline Using CASSCF and XMCQDPT2 Electronic Structure Calculations

2016

In this chapter, the tools introduced in Chap. 2 are applied to the study of the photochemistry of aniline. This work has been initiated during a six-month fellowship in the group of Professor Helen Fielding in the Chemistry Department of University College London, in the framework of the FASTQUAST Initial Training Network.

Equilibrium Geometry of the Ethynyl (CCH) Radical

2004

The equilibrium geometry of the ethynyl (CCH) radical has been obtained using the results of high-level quantum chemical calculations and the available experimental data. In a purely quantum chemical approach, the best theoretical estimates (1.208 A for r C C and 1.061-1.063 A for r C H ) have been obtained from CCSD-(T), CCSDT, MR-AQCC, and full CI calculations with basis sets up to core-polarized pentuple-zeta quality. In a mixed theoretical-experimental approach, empirical equilibrium geometrical parameters (1.207 A for r C C and 1.069 A for r C H ) have been obtained from a least-squares fit to the experimental rotational constants of four isotopomers of CCH which have been corrected fo…

Rotational spectrum of silyl chloride: hyperfine structure and equilibrium geometry

2012

The Lamb-dip technique was employed to record the rotational spectra of two isotopic species of silyl chloride, namely (28)SiH3Cl and (29)SiH3Cl, in order to investigate their hyperfine structure. High-accuracy quantum-chemical computations were employed to predict the hyperfine parameters involved and to support the experimental investigation. Analysis of the experimental spectra led to an improvement in the accuracy of the known spectroscopic constants as well as allowed us to determine additional spectroscopic parameters for the first time. Furthermore, the equilibrium structure of silyl chloride was reinvestigated using both theoretical and experimental data. The best theoretical and se…