COMMISSION ON MOLECULAR STRUCTURE AND SPECTROSCOPY (I.5)
Title: The Computation of Experimental Structure
and Properties of Small Molecules by Ab Initio Calculation
Janoschek and M.
Completion Date: 2001 - project completed
This is the first project in theoretical chemistry that Commission
I.5 has proposed. It is therefore appropriate to establish the current
state of ab initio calculations for the molecules for which calculations
are expected to be the most successful, namely small molecules. The
objective is to examine the agreement obtained between different ab
initio calculations and the best experimental data, and to produce
a summary that defines the successful methods and draws attention
to the generalizations that can be made and those that are not valid.
It is proposed to work out a list of two-, three-, and four-atomic
molecules, and even larger systems, in which the most sophisticated
computational results for structure and spectroscopy are given and
compared with the best experimental results available. The list will
be finite and the study will provide a basis of fact that should enhance
the knowledge of experimentalists about the demonstrated accuracy
of ab initio calculations and provide a basis for theoretical extension
to larger molecules. The list will provide a partial answer to the
important question that is regularly asked by experimentalists "To
what extent are ab initio calculations reliable?". The study will
also lead naturally into questions of nomenclature, symbols and standards,
which will have to be resolved to provide consistency within the report.
The scope of the project originally proposed has been carefully evaluated.
The results in the current literature do not permit a systematic comparison
of different computational methods for specific molecular properties.
There is too little consistency in the level of theory used to make
the comparison useful. Accordingly, the goal was changed while remaining
within the scope of the project. The new goal is to systematically
calculate the most important physical properties of diatomic and selected
triatomic molecules by the best current density-functional theory.
The goal is to determine the predictive power of this recently developed
quantum chemical method, using the experimental data as a gauge, and
to show the usefulness of calculated properties for those unstable
diatomic systems for which experimental information is incomplete.
A 79 page report was reviewed by the Commission at the
1997 General Assembly in Geneva. The report contained the calculated
results for almost 200 diatomic molecules compared with experimental
data. Many changes and additions were made to incorporate the Commissioner's
comments and a presentation of the updated report was made to the
Commission in Berlin. The final report is in preparation and will
be submitted to the Commissioners for approval. The goal is for publication
Project completed - A Technical Report entitled 'Quantum
chemical B3LYP/cc-pvqz computation of ground-state structures and
properties of small molecules with atoms of Z £
18 (hydrogen to argon) is published in Pure
73(9), pp. 1521-1553, 2001.
Last update: 30 November 2001