English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

Full Configuration Interaction Quantum Monte Carlo (FCIQMC) has beeneffectively applied to very large configuration interaction (CI) problems, andwas recently adapted for use as an active space solver and combined withorbital optimisation. In this work, we detail an approach within FCIQMC toallow for efficient sampling of fully internally-contracted multireferenceperturbation theories within the same stochastic framework. Schemes aredescribed to allow for the close control over the resolution of stochasticsampling of the effective higher-body intermediates within the active space. Itis found that while CASPT2 seems less amenable to a stochastic reformulation,NEVPT2 is far more stable, requiring a similar number of walkers to convergethe NEVPT2 expectation values as to converge the underlying CI problem. Wedemonstrate the application of the stochastic approach to the computation ofNEVPT2 within a (24,24) active space in a biologically relevant system, andshow that small numbers of walkers are sufficient for a faithful sampling ofthe NEVPT2 energy to chemical accuracy, despite the active space alreadyexceeding the limits of practicality for traditional approaches. This raisesprospects of an efficient stochastic solver for multireference chemicalproblems requiring large active spaces, with an accurate treatment of externalorbitals.

journal of chemical physics online/the journal of chemical physics/journal of chemical physics

Efficient and Stochastic Multireference Perturbation Theory for Large  Active Spaces within a Full Configuration Interaction Quantum Monte Carlo  Framework