Multicomponent Coupled Cluster Singles and Doubles with Density Fitting: Protonated Water Tetramers with Quantized Protons

2021 ◽  
Vol 12 (6) ◽  
pp. 1631-1637
Author(s):  
Fabijan Pavošević ◽  
Zhen Tao ◽  
Sharon Hammes-Schiffer
Keyword(s):  
Coupled Cluster ◽  
Density Fitting

Orbital-optimized linearized coupled-cluster doubles with density-fitting and Cholesky decomposition approximations: an efficient implementation

2016 ◽  
Vol 18 (16) ◽  
pp. 11362-11373 ◽  
Author(s):  
Uğur Bozkaya
Keyword(s):  
Cholesky Decomposition ◽  
Efficient Implementation ◽  
Coupled Cluster ◽  
Density Fitting

An efficient implementation of the orbital-optimized linearized coupled-cluster double method with the density-fitting (DF-OLCCD) and Cholesky decomposition (CD-OLCCD) approximations is presented.

scholarly journals Energy and Analytic Gradients for the Orbital-Optimized Coupled-Cluster Doubles Method with the Density-Fitting Approximation: An Efficient Implementation

2020 ◽  
Author(s):  
Uğur Bozkaya ◽  
Aslı Ünal ◽  
Yavuz Alagöz
Keyword(s):  
Hydrogen Transfer ◽  
Computational Cost ◽  
Linear Response Theory ◽  
Open Shell ◽  
Basis Set ◽  
Computational Time ◽  
Coupled Cluster ◽  
Chemical Systems ◽  
Density Fitting ◽  
Near Degeneracy

Efficient implementations of the orbital-optimized coupled-cluster doubles [or simply ``optimized CCD'', OCCD, for short] method and its analytic energy gradients with the density-fitting (DF) approach, denoted by DF-OCCD, are presented. In addition to the DF approach, the Cholesky-decomposed variant (CD-OCCD) is also implemented for energy computations. The computational cost of the DF-OCCD method is compared with that of the conventional OCCD. In the conventional OCCD, one needs to perform four-index integrals transformations at each CCD iterations, which limits its applications to large chemical systems. Our results demonstrate that DF-OCCD provides significantly lower computational costs compared to OCCD, there are almost 7-fold reductions in the computational time for the \ce{C5H12} molecule with the cc-pVTZ basis set. For open-shell geometries, interaction energies, and hydrogen transfer reactions, DF-OCCD provides significant improvements upon DF-CCD. Further, several factors make DF-OCCD more attractive compared to CCSD: (1) for DF-OCCD there is no need for orbital relaxation contributions in analytic gradient computations (2) active spaces can readily be incorporated into DF-OCCD (3) DF-OCCD provides accurate vibrational frequencies when symmetry-breaking problems are observed (4) in its response function, DF-OCCD avoids artificial poles; hence, excited-state molecular properties can be computed via linear response theory (5) Symmetric and asymmetric triples corrections based on DF-OCCD [DF-OCCD(T)] has a significantly better performance in near degeneracy regions.

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