ID:
713878.0,
MPI für bioanorganische Chemie / MPI für bioanorganische Chemie 
Speeding up equation of motion coupled cluster theory with the chain of spheres approximation 
Authors:  Dutta, Achintya Kumar; Neese, Frank; Izsak, Robert 
Language:  English 
Date of Publication (YYYYMMDD):  2016 
Title of Journal:  Journal of Chemical Physics 
Journal Abbrev.:  J.Chem.Phys. 
Volume:  144 
Issue / Number:  3 
Start Page:  0341021 
End Page:  03410213 
Sequence Number of Article:  034102 
Review Status:  Internal review 
Audience:  Experts Only 
Abstract / Description:  In the present paper, the chain of spheres exchange (COSX) approximation is applied to the highest scaling terms in the equation of motion (EOM) coupled cluster equations with single and double excitations, in particular, the terms involving integrals with four virtual labels. It is found that even the acceleration of this single term yields significant computational gains without compromising the desired accuracy of the method. For an excitation energy calculation on a cluster of five water molecules using 585 basis functions, the four virtual term is 9.4 times faster using COSX with a loose grid than using the canonical implementation, which yields a 2.6 fold acceleration for the whole of the EOM calculation. For electron attachment calculations, the four virtual term is 15 times and the total EOM calculation is 10 times faster than the canonical calculation for the same system. The accuracy of the new method was tested using Thiel's test set for excited states using the same settings and the maximum absolute deviation over the whole test set was found to be 12.945 cm(1) (59 mu Hartree) for excitation energies and 6.799 cm(1) (31 mu Hartree) for electron attachments. Using MP2 amplitudes for the ground state in combination with the parallel evaluation of the full EOM equations in the manner discussed in this paper enabled us to perform calculations for large systems. Electron affinity values for the two lowest states of a Zn protoporphyrine model compound (224 correlated electrons and 1120 basis functions) were obtained in 3 days 19 h using 4 cores of a Xeon E52670 processor allocating 10 GB memory per core. Calculating the lowest two excitation energies for transretinal (114 correlated electrons and 539 basis functions) took 1 day 21 h using eight cores of the same processor and identical memory allocation per core. (C) 2016 AIP Publishing LLC. 
Comment of the Author/Creator:  Date: 2016, JAN 21 2016 
External Publication Status:  published 
Document Type:  Article 
Communicated by:  N. N. 
Affiliations:  MPI für bioanorganische Chemie

Identifiers:  ISI:000368619100005 [ID No:1] ISSN:00219606 [ID No:2] DOI:10.1063/1.4939844 [ID No:3] 
