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Analysis of the errors in explicitly correlated electronic structure theory.
Andrew J May1, Edward Valeev, Robert Polly
1School of Chemistry, University of Bristol, Cantocks Close, Bristol, UK.
Physical Chemistry Chemical Physics : PCCP
|September 29, 2005
Summary
Explicitly correlated second-order Møller-Plesset (MP2-R12) methods offer high accuracy but face limitations in larger systems. The primary error source in these calculations is the choice of the correlation factor r12.
Area of Science:
- Quantum Chemistry
- Computational Chemistry
- Theoretical Chemistry
Background:
- Explicitly correlated methods, such as second-order Møller-Plesset (MP2-R12), achieve high accuracy by incorporating interelectronic distances.
- Conventional MP2 calculations struggle to reach the basis set limit for larger systems, necessitating more advanced techniques.
Purpose of the Study:
- To analyze the sources of error in MP2-R12 calculations when using basis sets practical for larger molecular systems.
- To identify key factors affecting the accuracy of MP2-R12 methods in computationally demanding scenarios.
Main Methods:
- Analysis of MP2-R12 calculations using practical basis sets (triple- or quadruple-zeta).
- Investigation of error contributions related to the correlation factor (r12), exchange commutators, and Brillouin conditions.
Main Results:
- MP2-R12 methods, while accurate for correlation cusps, do not fully bridge the gap to the MP2 basis set limit in practical basis sets.
- The choice of the correlation factor r12 is identified as the primary source of error.
- Neglecting exchange commutators and the extended Brillouin condition are significant error sources.
Conclusions:
- The accuracy of MP2-R12 calculations in practical basis sets is critically dependent on the selection of the correlation factor.
- Avoiding the neglect of exchange commutators and the extended Brillouin condition is crucial for reliable quantum chemical results.
- The generalized Brillouin condition does not introduce significant errors.
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