Automated generation of coupled-cluster diagrams: Implementation in the multireference state-specific coupled-cluster approach with the complete-active-space reference

Abstract

An algorithm for generation of the spin-orbital diagrammatic representation, the corresponding algebraical formulas, and the computer code of the coupled-cluster (CC) method with an arbitrary level of the electronic excitations has been developed. The method was implemented in the general case as well as for specific application in the state-specific multireference coupled-cluster theory (SSMRCC) based on the concept of a "formal reference state." The algorithm was tested in SSMRCC calculations describing dissociation of a single bond and in calculations describing simultaneous dissociation of two single bonds--the problem requiring up to six-particle excitations in the CC operator.

Block Correlated Coupled Cluster Theory With A Complete Active-Space Self-Consistent-Field Reference Function: The General Formalism And Applications

“…The CASPT2 method provides the smallest NPE (0.6 mH) in this molecule, although the absolute deviation is considerably larger than that of CAS-BCCC4. The simultaneous dissociation in H 2 O is a typical double-bond breaking model, which has been widely investigated [40,45,112,113,118,159,160]. In our calculations, we fix the bond angle at 109.57 • , and stretch two O H bonds symmetrically to the dissociation limit.…”

An efficient tensor transpose algorithm for multicore CPU, Intel Xeon Phi, and NVidia Tesla GPU

“…Only the internal element order in a tensor block will be modified according to a given permutation, that is, a tensor block will be transposed into another tensor block. In the current work, we restrict ourselves to dense tensor blocks, although partially ordered tensor block storage schemes (with partial order relations between tensor dimensions) are extremely important when dealing with higher-rank tensors encountered in multireference quantum many-body theory [28][29][30][31][32][33][34][35][36][37][38]. The implementation of the corresponding (partially ordered) tensor transpose algorithms will be reported elsewhere.…”

“…To improve efficiency, one can try using in-place reordering algorithms [27] (if memory bound) or employ optimized generic sorting algorithms, especially for tensors of lower dimensionality (say, up to four). However, there is a whole class of high-end correlated many-body theories [28][29][30][31][32][33][34][35][36][37][38] where the tensor dimensionality can grow really high, thus increasing the size of the sorted keys. Consequently, the main objective of this work is to introduce an alternative, cache-efficient, parallel tensor transpose algorithm (as a part of the tensor contraction operation) capable of running on multicore compute nodes, possibly equipped with the Intel Xeon Phi and NVidia GPU accelerators.…”

State-specific multireference complete-active-space coupled-cluster approach versus other quantum chemical methods: dissociation of the N2molecule

“…Our work on the MRCC approach has resulted in development of several distinct methods, which we called CASCCD [16,17] and CAS(n,m)CCSD [18]. They have been derived from the approaches proposed in the earlier works of Oliphant and Adamowicz [13] and Piecuch and co-workers [19,20].…”

“…A coupled-cluster analogue to CASCISD is the CASCCSD approach [18,27,30], which can be viewed as an extension of CASCISD that incorporates the sizeextensivity in the description of the electron correlation. The disadvantage of the approach is that it is more computationally demanding than CASCISD and the wave function ansatz is not invariant with respect to the choice of the Fermi vacuum.…”