Single reference methods

Choosing Electronic Structure Methods for Conical Intersections 

The development of analytic gradient techniques enables the efficient characterization of PESs by finding optimized structures for molecules, locating transition states, and establishing reaction pathways. Applications of analytical 

This method has been implemented using analytic gradients from MRCI wave-functions and has recently been added to the COLUMBUS suite of programs/  

The derivative coupling can be calculated for Cl or for MCSCF wave-functions using analytic gradients from the expression  

The list of systems in which conical intersections have been studied is lengthy and one cannot account for all of them in a chapter like this. Here it is pointed out that most areas of chemistry are affected by conical intersections. Examples related to the author s own research will be described in greater detail later to illustrate how conical intersections can be used to understand mechanisms of photophysical or photochemical processes. 

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A different approach for calculating excited states is based on indirect methods that allow one to calculate excitation energies based on a single reference wavefunction. Single reference methods for the calcualtion of excited states of large molecules have... 

In summary, it can be said that multireference Cl methods provide a balanced description of static and dynamic correlation effects. This comes at the cost of a considerably increased computational demand compared to single-reference methods. Nevertheless, a multireference approach is inevitable for systems with a genuine multiconfigurational character such as symmetric transition metal compounds. 

We may note a number of features of these results. First, nondynamical correlation is known to be much more important in the singlet state than in the triplet. Hence it is not surprising that the multireference methods perform better here than the single reference methods. Nevertheless, the errors in the single reference meth-... 

There are several single reference methods to compute electronic transition energies. Among them are configuration interaction-singles (CIS) [48], random-phase approximation (RPA) [49, 50], equation-of-motion couple cluster (EOMCC)... 

SINGLE-REFERENCE METHODS FOR EXCITED STATES IN MOLECULES AND POLYMERS... 

Single-Reference Methods for Excited States in Molecules and Polymers... 

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