Recursively generated intermediates

By following the algorithm described in Figure 3 and by using the idea of recursively generated intermediates in the calculation of the triply excited moments Table 1) and the CR-EOMCCSD(T)... 

A few approximate EOMXCCSD schemes, such as the PE3 method for electronically excited states discussed in Sections 5 and 6, have been considered in detail. The final equations of the PE3 scheme have been presented in a fully factorized form using recursively generated intermediates. In this way, we should be able to achieve the optimum performance, once the PE3 method is implemented, since each intermediate can be represented as a product of two arrays, which can be very efficiently evaluated using fast matrix multiplication routines. All EOMXCCSD approximations are n6 procedures, even though we may encounter terms which scale as n0n or n . The most expensive n terms (there are only two terms which scale as n ) can likely be discarded since they have no relationship with the T3 contributions of the standard EOMCC formalism. 

The above expressions for h (l, 2) and h (l, 2) are defined in terms of recursively generated intermediates [92], which we list below,... 

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