Communication: The distinguishable cluster approximation

Abstract

The equation of motion coupled-cluster method. A systematic biorthogonal approach to molecular excitation energies, transition probabilities, and excited state properties The Journal of Chemical Physics 98, 7029 (1993) We present a method that accurately describes strongly correlated states and captures dynamical correlation. It is derived as a modification of coupled-cluster theory with single and double excitations (CCSD) through consideration of particle distinguishability between dissociated fragments, whilst retaining the key desirable properties of particle-hole symmetry, size extensivity, invariance to rotations within the occupied and virtual spaces, and exactness for two-electron subsystems. The resulting method, called the distinguishable cluster approximation, smoothly dissociates difficult cases such as the nitrogen molecule, with the modest N 6 computational cost of CCSD. Even for molecules near their equilibrium geometries, the new model outperforms CCSD. It also accurately describes the massively correlated states encountered when dissociating hydrogen lattices, a proxy for the metalinsulator transition, and the fully dissociated system is treated exactly. © 2013 AIP Publishing LLC.

Can Single-Reference Coupled Cluster Theory Describe Static Correlation?

“…Numerous authors have proposed methods that yield reasonable predictions in the presence of near degeneracies by modifying coupled cluster theory or variants thereof. [8][9][10][11][12][13][14][15][16][17][18][19][20] We would like a simple conceptual framework which allows us to identify the offending terms in traditional coupled cluster theory so that by excluding them we can avoid the downfall of the method. Of course, this is easier said than done, but we here show one particular case which substantially removes the typical failures in repulsive Hamiltonians.…”

Attenuated coupled cluster: a heuristic polynomial similarity transformation incorporating spin symmetry projection into traditional coupled cluster theory

“…[14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] In previous work along these lines, we found that separating the singlet-and triplet pairing channels of T 2 and isolating them from one another, giving singlet-paired (CC0) and triplet-paired coupled cluster (CC1), protected CC from blowup. [27,29] There, we decomposed T 2 along particle-particle/holehole (pp-hh), or ladder, channels, [30] eliminating the interaction of the channels completely.…”

Rotational Brownian Dynamics simulations of clathrin cage formation

“…Relaxing orbitals for DCD using Brueckner condition [10][11][12] was considered in Paper I. 8 Although a DCD wavefunction cannot be properly specified, one can formally assume that there is a DCD wavefunction containing only doubles, and then the orbitals are rotated such that the condition…”

“…There are many attempts to develop methods capable to treat strong correlation in the single-reference framework. [2][3][4][5][6][7] Very recently we have proposed a method named the distinguishable cluster doubles (DCD) approximation, 8 which retains the simplicity and efficiency of the single-reference treatment, but is accurate and robust in the strongly correlated cases, e.g., in bond-breaking processes. Furthermore, even in single-reference cases the accuracy of DCD turned out to be superior to the conventional CCD counterpart.…”