On the evaluation of non-Born--Oppenheimer interactions for Born--Oppenheimer wave functions. V. A body fixed frame approach. Applications to isotope effects on equilibrium geometries and the adiabatic correction for the X /sup 1/. sigma. /sup +/ state of LiH

Journal Article · Fri Jul 15 04:00:00 EDT 1988 · J. Chem. Phys.; (United States)

OSTI ID:7148330

Jensen, J O; Yarkony, D R

The evaluation of the total second derivative nonadiabatic coupling matrix element H(J,I,R) = /sub r/ is considered. Here psi/sub J/(r;R) is the adiabatic Born--Oppenheimer electronic wave function which in this work will be approximated by a large-scale CI wave function developed from an MCSCF reference space. For diatomic and triatomic systems the computational effort associated with the evaluation of H(J,I,R) can be reduced considerably by the use of a body fixed frame approach. In this approach costly evaluation of the derivative wave function with respect to noninternal degrees of freedom in the space fixed frame is replaced by the evaluation of matrix elements of many electron operators including the mass polarization operator (total electronic linear momentum squared) and the L/sup 2/ operator (total electronic orbital angular momentum squared). The equivalence of the body fixed frame and space fixed frame results leads to valuable diagnostic equations which provide stringent tests of the derivative methodology used to evaluate the remaining second derivatives with respect to internal coordinates. The methods presented here are applied to the benchmark systems BeH/sup +/ and LiH. The Born--Oppenheimer diagonal correction or adiabatic correction (AC) is evaluated for the X /sup 1/summation/sup +/ state of these systems and used to consider the effect of isotopic substitution on equilibrium geometries. For the X /sup 1/summation/sup +/ state of LiH a troubling discrepancy exists between the AC determined by advanced theoretical and experimental techniques.

• Research Organization: Chemical Research, Development and Engineering Center, SMCCR-RSP-C, Aberdeen Proving Ground, Maryland 21010-5423
• OSTI ID: 7148330
• Journal Information: J. Chem. Phys.; (United States), Journal Name: J. Chem. Phys.; (United States) Vol. 89:2; ISSN JCPSA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400202* -- Isotope Effects
Isotope Exchange
& Isotope Separation
ALKALI METAL COMPOUNDS
ALKALI METAL ISOTOPES
BORN-OPPENHEIMER APPROXIMATION
CONFIGURATION INTERACTION
CORRECTIONS
DEUTERIUM
ELECTRONIC STRUCTURE
HYDRIDES
HYDROGEN COMPOUNDS
HYDROGEN ISOTOPES
ISOTOPE EFFECTS
ISOTOPES
LIGHT NUCLEI
LITHIUM 6
LITHIUM 7
LITHIUM COMPOUNDS
LITHIUM HYDRIDES
LITHIUM ISOTOPES
MOLECULAR STRUCTURE
NUCLEI
ODD-EVEN NUCLEI
ODD-ODD NUCLEI
STABLE ISOTOPES