Partition of electronic excitation energies: the IQA/EOM-CCSD method

Fernández‐Alarcón, Alberto; Casals‐Sainz, José Luis; Guevara‐Vela, José Manuel; Costales, Aurora; Francisco, E.; Pendás, Ángel Martín; Rocha‐Rinza, Tomás

doi:10.1039/c9cp00530g

Cited by 20 publications

(30 citation statements)

References 52 publications

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“…The local energetic effects of the S 0 !S 1 transition in the H 2 Om onomer are summarised in Ta xc ,t he greater DI in the excited state does not indicate ar ise in normalc ovalency,b ut indicates insteada ni ncreaseo ft he zwitterionic character of the interaction, as we have shown in other cases recently. [63,68] Very briefly,f or az witterionic resonance, such as H + ÀH À $H À ÀH + in H 2 ,t here are only two possibilities for atomic populations, namely,b oth electrons are located in any of the two interacting Ha toms. In such ac ase, the fluctuation of the electron population is maximum and the DI rises to two, even for at wo-centred two-electron (2c,2e) chemical bond.…”

Section: Resultsmentioning

confidence: 99%

“…We have recently proposed am ethodt od issecte xcitation energies computed with the black-box equation-of-motion (EOM) coupled-cluster singles and doubles (CCSD) approximationi nto atomica nd interatomic contributions by using the IQA formalism. [63] This new approach, denoted as IQA/EOM-CCSD, is particularly suitable for the examination of EESso fm olecular clusters, such as (H 2 O) 2 ,b ecauseo ft he size consistency of the EOM-CCSD excitation energies. The coupling of this electronic structure approximation with IQA provides au nique way to detect which atoms and interactions are activated or depleted by photoabsorptioni nm olecules andmolecular clusters.…”

Section: Introductionmentioning

confidence: 99%

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Photochemistry in Real Space: Batho‐ and Hypsochromism in the Water Dimer

Fernández‐Alarcón

Guevara‐Vela

Casals‐Sainz

et al. 2020

Chemistry A European J

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The development of chemical intuition in photochemistry faces several difficulties that result from the inadequacy of the one‐particle picture, the Born–Oppenheimer approximation, and other basic ideas used to build models. It is shown herein how real‐space approaches can be efficiently used to gain valuable insights in photochemistry through a simple example of red and blue shift effects: the double hypso‐ and bathochromic shifts in the low‐lying valence excited states of (H2O)2. It is demonstrated that 1) the use of these techniques allows the perturbative language used in the theory of intermolecular interactions, even in the strongly interacting short‐range regime, to be maintained; 2) one and only one molecule is photoexcited in each of the addressed excited states and 3) the electrostatic interaction between the in‐the‐cluster molecular dipoles provides a fairly intuitive rationalisation of the observed batho‐ and hypsochromism. The methods exploited and illustrated herein are able to maintain the individuality and properties of the interacting entities in a molecular aggregate, and thereby they allow chemical intuition in general states, at any geometry and using a broad variety of electronic structure methods to be kept and built.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Photochemistry in Real Space: Batho‐ and Hypsochromism in the Water Dimer

Fernández‐Alarcón

Guevara‐Vela

Casals‐Sainz

et al. 2020

Chemistry A European J

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“…Actually, in order for IQA to be used, it only requires the knowledge of the one-particle and (diagonal) two-particle density matrices, although molecular descriptions at the DFT level are also possible in the IQA context. Finally, although IQA has, to date, been applied almost exclusively in the ground electronic state, we have also recently started to use it in excited electronic states [83,84].…”

Section: Discussionmentioning

confidence: 99%

Tetrel Interactions from an Interacting Quantum Atoms Perspective

et al. 2019

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Tetrel bonds, the purportedly non-covalent interaction between a molecule that contains an atom of group 14 and an anion or (more generally) an atom or molecule with lone electron pairs, are under intense scrutiny. In this work, we perform an interacting quantum atoms (IQA) analysis of several simple complexes formed between an electrophilic fragment (A) (CH3F, CH4, CO2, CS2, SiO2, SiH3F, SiH4, GeH3F, GeO2, and GeH4) and an electron-pair-rich system (B) (NCH, NCO-, OCN-, F-, Br-, CN-, CO, CS, Kr, NC-, NH3, OC, OH2, SH-, and N3-) at the aug-cc-pvtz coupled cluster singles and doubles (CCSD) level of calculation. The binding energy ( E bind AB ) is separated into intrafragment and inter-fragment components, and the latter in turn split into classical and covalent contributions. It is shown that the three terms are important in determining E bind AB , with absolute values that increase in passing from electrophilic fragments containing C, Ge, and Si. The degree of covalency between A and B is measured through the real space bond order known as the delocalization index ( δ AB ). Finally, a good linear correlation is found between δ AB and E xc AB , the exchange correlation (xc) or covalent contribution to E bind AB .

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“…Although until recently the IQA methodology had been applied to molecular systems in the ground electronic state, there is nothing preventing its application in excited electronic states [ 26 ]. Very recently, the black-box equation-of-motion (EOM) coupled-cluster singles and doubles (CCSD) approximation has been used to construct

and

and to use the IQA method to dissect excitation energies into atomic and interatomic contributions of molecular clusters such as (H

, getting very valuables insights in photochemistry.…”

Section: The Iqa Methodologymentioning

confidence: 99%

Interacting Quantum Atoms—A Review

et al. 2020

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The aim of this review is threefold. On the one hand, we intend it to serve as a gentle introduction to the Interacting Quantum Atoms (IQA) methodology for those unfamiliar with it. Second, we expect it to act as an up-to-date reference of recent developments related to IQA. Finally, we want it to highlight a non-exhaustive, yet representative set of showcase examples about how to use IQA to shed light in different chemical problems. To accomplish this, we start by providing a brief context to justify the development of IQA as a real space alternative to other existent energy partition schemes of the non-relativistic energy of molecules. We then introduce a self-contained algebraic derivation of the methodological IQA ecosystem as well as an overview of how these formulations vary with the level of theory employed to obtain the molecular wavefunction upon which the IQA procedure relies. Finally, we review the several applications of IQA as examined by different research groups worldwide to investigate a wide variety of chemical problems.

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Partition of electronic excitation energies: the IQA/EOM-CCSD method

Abstract: We put together equation of motion coupled cluster theory and the interacting quantum atoms electronic energy partition to determine how an absorbed photon changes atomic energies as well as covalent and noncovalent interactions within a molecule or molecular cluster.

Cited by 20 publications

References 52 publications

Photochemistry in Real Space: Batho‐ and Hypsochromism in the Water Dimer

Photochemistry in Real Space: Batho‐ and Hypsochromism in the Water Dimer

Tetrel Interactions from an Interacting Quantum Atoms Perspective

Interacting Quantum Atoms—A Review

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