By adding a negative imaginary potential of variable strength eta to the Hamiltonian, the resonance state of a system can be found as complex energy stabilized points in the eta-trajectories of the eigenvalues. One problem that arises in practical calculations is the appearance of nonphysical complex energy stabilized points. A new method for separating the physical from the nonphysical complex energy stabilized points is proposed. The method is best illustrated with strongly correlated two-electron systems.
In low-energy electron impact on neutral molecules, the free electron and the molecule often form an intermediate metastable electron-molecule compound. [1][2][3] This compound may either release the excess electron by autodetachment (AD) [1] or fragment by a reaction called dissociative electron attachment [DEA, Eq. (1)]: [1][2][3] e À þ AB ! ðABÞA wide variety of chemical transformations initiated by electron impact can be attributed to DEA. [1][2][3] In particular, it is well known that in organic molecules DEA efficiently leads to bond dissociation, producing radical and radical-anion molecular fragments. In general, in all examples studied and understood theoretically, DEA leads to an anionic fragment and a neutral fragment. [1][2][3] Recently, mass spectroscopic measurements monitoring DEA of fructose have shown that several neutral fragments may appear in addition to the anionic fragment.[4] The underlying mechanisms have not been clarified yet, but it may be suspected from the detected products that the two fragments initially formed by DEA as in Equation (1) have further fragmented by several stepwise reactions. In any case, electron-molecule reactions are seen to be chemically rich and are of chemical interest.Herein we report on a new elementary reaction (i.e., single-step reaction) mechanism of an electron and a molecule in a metastable compound which we call (two or more) bond breaking by a catalytic electron (BBCE). Unlike in DEA, the formed compound anion dissociates into nonradical neutral molecular subunits and a free electron, which plays the role of a catalyst [Eq. (2)]:where we stress that at least two bonds (not a double bond) break in the elementary reaction path. Notice that the electron is freed in the course of the elementary reaction, that is, the electron is not attached to any of the chemical products of the elementary reaction and, thus, we refer to this mechanism as an electron-catalyzed mechanism. This elementary reaction involves both bond breaking and detachment of the electron. The key differences between BBCE and DEA are as follows: 1. More than one s bond (two-center bond) is broken in the elementary BBCE reaction. 2. The products formed in the BBCE are neutral. 3. The electron is released in the course of the elementary BBCE reaction.Below, we illustrate this mechanism more precisely by investigating electron impact on the quadricyclanone (QDCO) molecule. As will become clearer, the low-energy electron impact on QDCO can be viewed as proceeding via a compound negative ion metastable state. We have acquired considerable experience in the ab initio computation of energy and lifetime of metastable anions using non-Hermitian quantum chemical methods. [5][6][7] Recently, the introduction of a so-called continuum remover complex absorbing potential [8] and its implementation in Greens function methods [9] have made non-Hermitian quantum chemical methods applicable to larger systems. The efficient identification of the metastable states and the correct scaling of the electronic ener...
The reflection-free complex absorbing potential (RF-CAP) method has been already applied to the study of the autoionization resonance of helium [Sajeev et al., Chem. Phys. 329, 307 (2006)]. The present work introduces a systematic way for implementing RF-CAP for the electronic structure calculations using Gaussian basis sets for molecules. As a test case study we applied the RF-CAP method to the lowest (1)Sigma(g) (+) and (1)Sigma(u) (+) Feshbach-type autoionization resonances of hydrogen molecule. Since thin RF-CAP absorbs fast electrons much better than the slow ones, a weak dc field has been added to the RF-CAP in the peripheral region of the molecule.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.