Topics

Automatic Active Space Selection for Calculating Electronic Excitation Energies Based on High-Spin Unrestricted Hartree-Fock Orbitals.

08:00 EDT 14th August 2019 | BioPortfolio

Summary of "Automatic Active Space Selection for Calculating Electronic Excitation Energies Based on High-Spin Unrestricted Hartree-Fock Orbitals."

Multireference perturbation theory (MR-PT2, e.g., MS-CASPT2) and multiconfiguration pair-density functional theory (MC-PDFT) use a multiconfigurational wave function as the reference wave function, and this can be generated, for example, by the complete active space self-consistent field (CASSCF) method or restricted active space self-consistent field (RASSCF) method. The MR-PT2 and MC-PDFT methods have proved successful in many previous studies, but their performance depends on the quality of the reference wave function, and the quality of a CASSCF or RASSCF wave function depends on the active space. Even for a given number of active electrons and active orbitals, the orbitals obtained at the end of the self-consistent-field iterations of the CASSCF calculation may be different for different sets of initial guess orbitals. Consequently, it is a worthwhile goal to automate active space selection, including the choice of orbitals to start the iterations; and here we examine the question of whether we can devise a broadly applicable automatic scheme for producing guess orbitals that lead to an active space that gives accurate excitation energies. Such a scheme depends on target number of excitation energies that one is trying to calculate, and here our target is the first two spin-conserving excited electronic states of a closed-shell molecule or radical. For this target we propose a scheme called ABC2 for automatically selecting an active space for MC-PDFT calculations and MS-CASPT2 calculations; the scheme uses high-spin-state unrestricted Hartree-Fock (UHF) natural orbitals as guess orbitals. A novel feature of the ABC2 scheme is that it contains a reliability test that should be passed for the results to be considered reliable. This test requires that the MC-PDFT or CASPT2 excitation energy be within 1.1 eV of the CASSCF for the result to be considered reliable. We evaluated the performance of ABC2 for the two lowest excitation energies (or only the lowest when an accurate value of the second lowest state is not available) of sixteen singlet systems and ten doublet systems. We compared the performances of ABC2 to that of our previous ABC scheme, which finds active orbitals through a more expensive (multiconfigurational) excited-state calculation, to the use of ground-state UHF natural orbitals, and to the default scheme in OpenMolcas. We find that the new scheme is more robust than previous methods for a variety of systems.

Affiliation

Journal Details

This article was published in the following journal.

Name: Journal of chemical theory and computation
ISSN: 1549-9626
Pages:

Links

DeepDyve research library

PubMed Articles [13875 Associated PubMed Articles listed on BioPortfolio]

Benchmarks for Electronically Excited States with CASSCF Methods.

The accuracy of three different complete active space (CAS) self-consistent field (CASSCF) methods is investigated for the electronically excited-state benchmark set of Schreiber et al. J. Chem. Phys....

How to extract quantitative information on electronic transitions from the DFT "black box".

Electronic couplings and vertical excitation energies are crucial determinants of charge and excitation energy transfer rates in a broad variety of processes ranging from biological charge transfer to...

First Principle Prediction of Intramolecular Singlet Fission and Triplet Triplet Annihilation Rates.

Intramolecular singlet fission and triplet-triplet annihilation (TTA) has been experimentally observed and reported. However, problems remain in theoretically accounting for the corresponding intramol...

ωB2PLYP & ωB2GPPLYP: the first two double-hybrid density functionals with long-range correction optimized for excitation energies.

Double-hybrid density functionals are currently the most accurate density functionals for ground-state properties and electronic excitations. Nevertheless, the lack of a long-range correction scheme m...

autoCAS: A Program for Fully Automated Multiconfigurational Calculations.

We present our implementation autoCAS for fully automated multiconfigurational calculations, which we also make available free of charge on our webpages. The graphical user interface of autoCAS connec...

Clinical Trials [5576 Associated Clinical Trials listed on BioPortfolio]

Consequences of Doing What Should Not be Done in Primary Care

Retrospective observational study in a random selection of 5% of digital records active between 2014 and 2017 to quantify the frequency of Do not do primary care recommendations, calculati...

Comparison Between Electronic and Traditional Chest Drainage Systems

This study is designed to compare the electronic chest drainage system (Drentech Palm Evo) with the traditional system, both already in use in the clinical practice, in a cohort of patient...

Tradeoff Between Spatial and Temporal Resolution

In this study, investigators will examine how temporal rate processing might be affected when the width of neural excitation narrows. The manipulation of neural excitation width will be ac...

SCANCAP Scandinavian Automatic Capture Study

The primary objective of this study is to document the success rate of the automatic threshold testat pre-discharge in a normal pacemaker patient population implanted with Guidant Insignia...

Comparison of Manual Cardiopulmonary Resuscitation (CPR) Versus Automatic CPR Machine During Ambulance Transport.

This is a randomized controlled prospective study which assigned patient to receive manual CPR or automatic CPR machine use. The quality and efficacy between manual CPR and machine CPR wil...

Medical and Biotech [MESH] Definitions

Analysis of the energy absorbed across a spectrum of x-ray energies/wavelengths to determine the chemical structure and electronic states of the absorbing medium.

Data processing largely performed by automatic means.

Abnormally rapid heartbeats originating from one or more automatic foci (nonsinus pacemakers) in the HEART ATRIUM but away from the SINOATRIAL NODE. Unlike the reentry mechanism, automatic tachycardia speeds up and slows down gradually. The episode is characterized by a HEART RATE between 135 to less than 200 beats per minute and lasting 30 seconds or longer.

A loosely defined group of drugs that tend to increase behavioral alertness, agitation, or excitation. They work by a variety of mechanisms, but usually not by direct excitation of neurons. The many drugs that have such actions as side effects to their main therapeutic use are not included here.

Adverse of favorable selection bias exhibited by insurers or enrollees resulting in disproportionate enrollment of certain groups of people.

Quick Search


DeepDyve research library

Relevant Topic

Multiple Sclerosis MS
Multiple sclerosis (MS) is the most common disabling neurological condition affecting 100,000 young adults in the UK. The condition results from autoimmune damage to myelin, causing interference in nerve signaling. Symptoms experienced depend on the pa...


Searches Linking to this Article