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Application of improved virtual orbital based multireference methods to N2, LiF, and C4H6 systems
Sudip Chattopadhyay1, Rajat K Chaudhuri, Uttam Sinha Mahapatra
1Department of Chemistry, Bengal Engineering and Science University Shibpur, Howrah 711 103, India. sudip_chattopadhyay@rediffmail.com
The Journal of Chemical Physics
|January 7, 2009
Summary
Improved virtual orbital (IVO) methods, including IVO-MCQDPT and IVO-MRMPPT, reliably calculate molecular potential energy curves for N2, LiF, and butadiene. These computational chemistry techniques offer accurate predictions for molecular properties.
Area of Science:
- Quantum Chemistry
- Computational Chemistry
- Theoretical Chemistry
Background:
- Accurate calculation of molecular properties is crucial for understanding chemical reactions and material properties.
- Multiconfigurational methods are essential for describing systems with strong electron correlation.
- Improved Virtual Orbital (IVO) methods offer a way to enhance the efficiency and accuracy of traditional quantum chemical calculations.
Purpose of the Study:
- To assess the efficacy and reliability of the improved virtual orbital (IVO) complete active space configuration interaction (CASCI) based multiconfigurational quasidegenerate perturbation theory (MCQDPT) and its single-root version (IVO-MRMPPT).
- To apply these methods to calculate potential energy curves (PECs) for ground and excited states of N2, LiF, and C4H6 (butadiene).
- To evaluate the performance of IVO-CASCI for geometry optimization using numerical energy gradients.
Main Methods:
- Improved Virtual Orbital (IVO) complete active space configuration interaction (CASCI) based multiconfigurational quasidegenerate perturbation theory (MCQDPT).
- Single-root version of IVO-MCQDPT, termed IVO-MRMPPT.
- Application of IVO-CASCI with numerical energy gradients for geometry optimization.
Main Results:
- IVO-MRMPPT and IVO-MCQDPT provide smooth and reliable PECs for N2, LiF, and butadiene, consistent with standard high-level methods.
- The ionic-neutral curve crossing in LiF was accurately modeled using IVO-MCQDPT.
- Ground state spectroscopic constants for N2 and LiF, calculated using IVO-CASCI, show good agreement with experimental data and other correlated methods, with small errors in frequency and bond length.
Conclusions:
- The IVO-based MRMPPT and MCQDPT methods are effective and reliable for calculating potential energy curves of chemically relevant systems.
- IVO-CASCI, coupled with numerical gradients, is suitable for geometry optimizations and calculating spectroscopic constants.
- These IVO-based approaches represent a significant advancement in computational quantum chemistry for accurate molecular property prediction.
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