Improving Excited State Calculations with Initial Guesses

What is it about?

Researchers have found a new approach to reduce the total number of iterations required for an excited state calculation by up to 50%. This is achieved by using a simple rotation of old amplitudes into the space of new molecular orbitals, using the Kabsch algorithm. This method has a much lower error than the standard approach and leads to faster convergence of the Davidson algorithm. This method can be applied to both the amplitudes and the z-vector, and has been tested on two molecules, showing significant speed-ups in calculations.

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Why is it important?

This research is important because it presents a simple and efficient method to reduce the total number of iterations required for an excited state calculation by up to 50%. By using information gathered at one geometry and applying it to another geometry, chemists can expect to generate excited state optimized structures with a total wall time reduced by up to 30% without any approximations. This can significantly speed up the computation process, allowing researchers to focus on more complex and important problems. Key Takeaways: 1. A simple rotation of old amplitudes into the space of new molecular orbitals using the Kabsch algorithm can serve as an exceedingly good and stable guess for the excited state amplitudes, reducing the error by several orders of magnitude compared to not making any guess. 2. The Davidson algorithm converges dramatically faster to the relevant excited states in a consistently stable fashion when the novel guess amplitudes are used. 3. The method can be applied to the z-vector for similar effect, improving the calculation of gradients and dipole moments.