New implementations of MRCI in semiempirical frameworks

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Theoretical Chemistry

Background:

• Accurate electronic structure calculations are crucial for understanding molecular properties.
• Existing methods for multireference configuration interaction (MRCI) can be computationally expensive.
• Efficient implementation of MRCI is needed for larger and more complex systems.

Purpose of the Study:

• To implement multireference configuration interaction with single and double excitations (MRCISD) within a semiempirical framework.
• To develop analytic configuration interaction (CI) gradients for the implemented MRCI method.
• To improve the efficiency and reduce storage requirements of MRCI calculations.

Main Methods:

• Implementation of MRCISD using hole-particle symmetry.
• Development of a mixed driven model for computing coupling coefficients.
• Integration into a semiempirical computational framework.

Main Results:

• Successful implementation of MRCISD and its analytic CI gradients.
• Demonstrated higher efficiency in calculations compared to previous methods.
• Achieved reduced storage requirements for MRCI calculations.

Conclusions:

• The new semiempirical MRCI code offers a more efficient approach to electronic structure calculations.
• This method facilitates more complex molecular modeling with reduced computational cost.
• The implementation provides a valuable tool for theoretical and computational chemistry research.