Orbital optimization in the perfect pairing hierarchy. Applications to full-valence calculations on linear polyacenes

Abstract

We describe the implementation of orbital optimization for the models in the perfect pairing hierarchy [Lehtola et al, J. Chem. Phys. 145, 134110 (2016)]. Orbital optimization, which is generally necessary to obtain reliable results, is pursued at perfect pairing (PP) and perfect quadruples (PQ) levels of theory for applications on linear polyacenes, which are believed to exhibit strong correlation in the π space. While local minima and σ-π symmetry breaking solutions were found for PP orbitals, no such problems were encountered for PQ orbitals. The PQ orbitals are used for single-point calculations at PP, PQ and perfect hextuples (PH) levels of theory, both only in the π subspace, as well as in the full σπ valence space. It is numerically demonstrated that the inclusion of single excitations is necessary also when optimized orbitals are used. PH is found to yield good agreement with previously published density matrix renormalization group (DMRG) data in the π space, capturing over 95% of the correlation energy. Full-valence calculations made possible by our novel, efficient code reveal that strong correlations are weaker when larger bases or active spaces are employed than in previous calculations. The largest full-valence PH calculations presented correspond to a (192e,192o) problem.

19 pages, 4 figures

References in corpus (10)

• The radical character of the acenes: A density matrix renormalization group study
• Semistochastic Heat-bath Configuration Interaction method: selected configuration interaction with semistochastic perturbation theory
• Orbital Optimization in the Density Matrix Renormalization Group, with applications to polyenes and β-carotene
• A deterministic alternative to the full configuration interaction quantum Monte Carlo method
• The density matrix renormalization group for ab initio quantum chemistry
• An adaptive configuration interaction approach for strongly correlated electrons with tunable accuracy
• Electronic Ground State of Higher Acenes
• A general second order complete active space self-consistent-field solver for large-scale systems
• DMRG-SCF study of the singlet, triplet, and quintet states of oxo-Mn(Salen)
• Cost-effective description of strong correlation: efficient implementations of the perfect quadruples and perfect hextuples models

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• Seniority and Hierarchy Configuration Interaction for Radicals and Excited States
• MBE-CASSCF Approach for the Accurate Treatment of Large Active Spaces
• Connections between Richardson-Gaudin States, Perfect-Pairing, and Pair Coupled-Cluster Theory
• Coupled-cluster pairing models for radicals with strong correlations
• A Reusable Library for Second-Order Orbital Optimization Using the Trust Region Method
• Method for Calculating Excited Electronic States Using Density Functionals and Direct Orbital Optimization with Real Space Grid or Plane Wave Basis Set