Conventional Cluster Model Research Articles

The Interaction and De-Categorization of Word Meaning Categories—The Radical Stage of Word Meaning Evolution

This paper employs the framework of "dynamic categorization" from cognitive linguistics to examine a more radical phase of word meaning derivation. Specifically, it investigates the interaction between word meaning categories and de-categorization in order to elucidate the principles governing word meaning derivation. Through a comprehensive analysis of extensive Chinese and English corpora, our findings indicate that the interaction between word meaning categories primarily is manifested in two forms: (1) expansion between adjacent categories; (2) expansion between analogous categories. The expansion between adjacent categories encompasses linguistic, conceptual, and factual expansions, whereas expansion between analogous categories involves both objective and psychological similarities. Such interaction between word meaning categories may result in partial grammaticalization, antonymization, and polysemy. De-categorization, on the other hand, is primarily achieved through word conversion, grammaticalization, and subjectivization. These processes contribute to the evolution of word meaning beyond conventional clustering models, transitioning from concrete to abstract and from literal to figurative interpretations.

Open-boundary cluster model with a parameter-free complex absorbing potential.

In quantum chemical calculations of heterogeneous structures in solids, e.g., when an impurity is located on the surface, the conventional cluster model is insufficient to describe the electronic structure of substrates due to its finite size. The open-boundary cluster model (OCM) overcomes this problem by performing cluster calculations under the outgoing-wave boundary condition. In this method, a complex absorbing potential (CAP) is used to impose the boundary condition, but the CAP used in the previous studies required parameter optimization based on the complex variational principle. This study proposes and applies a parameter-free CAP to OCM calculations. This approach makes it possible to uniquely determine the band-specific CAP based on the surface Green's function theory. Using this CAP, we conducted OCM calculations of the tight-binding model of a one-dimensional semi-infinite chain, and we found that the calculated density of states agreed with the exact one. Surface states of the Newns-Anderson-Grimley model were also computed using the CAP, and the projected density of states on the adsorbed atom was successfully reproduced.

Performance Improvement of Clustering Affinity Propagation Method using Principal Component Analysis

Affinity Propagation Method it is necessary to modify the algorithm by using Principal Component Analysis (PCA). PCA method is used to reduce the attributes or characteristics that are less influential on the data so that the most influential attributes are obtained to then be carried out the clustering process with Affinity Propagation. The comparison results of the PCA + AP grouping model have better performance than the conventional AP grouping model. This is justified because the number of iterations and clusters produced by the PCA + AP clustering model does not change and converges when there are 8 optimal cluster clusters. While the performance of conventional clustering models produces an optimal number of clusters from 14 clusters with a significant number of iterations. So it can be concluded that the PCA + AP grouping model is suitable for the Air Quality dataset because it produces an optimal number of clusters and iterations of 8 clusters. The comparison results of the PCA + AP grouping model have better performance than the conventional AP grouping model. This is justified because the number of iterations and clusters produced by the PCA + AP clustering model does not change and converges when the optimal number of clusters is 5 clusters. While the performance of conventional clustering models produces a suboptimal number of 10 clusters with a significant number of iterations. So it can be concluded that the PCA + AP grouping model is suitable for the Water Quality Status dataset because it produces an optimal number of clusters and 5 cluster repetitions.

LDA+DMFT approach to core-level spectroscopy: Application to 3d transition metal compounds

We present a computational study of 2$p$ core-level X-ray photoemission spectra of transition metal monoxides MO (M=Ni, Co, Mn) and sesquioxides M$_2$O$_3$ (M=V, Cr, Fe) using a theoretical framework based on the local-density approximation (LDA) $+$ dynamical mean-field theory (DMFT). We find a very good description of the fine spectral features, which improves considerably over the conventional cluster model. We analyze the role of the non-local screening and its relationship to the long-range magnetic order and the lattice geometry. Our results reveal the potential of the present method for the analysis and interpretation of the modern high-energy-resolution experiments.

Exotic cluster structure in light nuclei

We discuss the appearance of various cluster structures in light nuclei. One of the examples is the appearance of geometric cluster configurations; gas-like α cluster states found in 12C and 16O could be stabilized with geometric shapes by adding neutrons or giving large angular momentum. We show in 16O that four α particles can have linear configurations with large angular momentum, which is very stable with respect to the bending motion using Skyrme cranked Hartree-Fock method. There exists a region of angular momentum (13-18 ℏ) where the linear chain configuration is stabilized. The calculated moment of inertia (ℏ2/2(-_ ~ 0.06-0.08 MeV) agrees well with conventional cluster model calculations. Another example of exotic cluster structure is the gas-like state of α clusters. The most famous example is the second 0+ state in 12C, the so called Hoyle state, which plays a dominant role in the synthesis of 12C and the heavier elements in the stars. We go one step further that such a dilute state of α particles exists around a strongly bound core in heavier systems. This study is performed by introducing a Monte Carlo technique for the description of the THSR (Tohsaki Horiuchi Schuck Röpke) wave function, and first we apply such method to three α state around a 40Ca core. Furthermore, coupling effect to other low-lying cluster states is taken into account; a large isoscalar monopole (E0) transition strength from the ground to the gas-like state is discussed in 24Mg. The gas-like state of two α clusters in 24Mg around the 16O core appears slightly below the 2α-thresliold energy.

Open-boundary cluster model implemented in first-principles calculations for electronic excited states of an adsorbate-surface system

Our recently developed open-boundary cluster model (OCM), which allows us to calculate electronic states of a semi-infinite adsorbate-surface system with a finite-small cluster, has been implemented in first-principles calculations to investigate excited states of a real system of a low-coverage Cs/Cu(111). The first-principles calculations are based on a real-space density functional theory (DFT) approach, and the Cs/Cu(111) system is reasonably represented in terms of a cluster of CsCu13 within the OCM approach. An absorption spectrum and the lifetime of excited states of the system are calculated successfully within the linear-response approximation, and the computed results qualitatively agree with experimental observations. Such excited properties are difficult to calculate by using a conventional cluster model (CCM) approach. Despite these advantages, the OCM-DFT approach requires a computational cost almost identical to the cost of CCM.

Properties of adsorbates as open quantum systems

We have recently developed a novel cluster-model approach to investigate adsorbate-surface systems. In our approach, a physically relevant subsystem is described as an open quantum system by considering a model cluster subject to the outgoing-wave boundary condition (OBC) at the edge of the cluster. We refer to this model as an open-boundary cluster model (OCM). Many known disadvantages of the conventional cluster-model approach, in which a model cluster is treated as an isolated system, have been remedied by introducing the OBC, whereas the local picture inherent in cluster models still remains valid. In our present research, the adsorption energy and the electron-transfer rate from adsorbates to surfaces are calculated with the OCM. Their dependences on the adsorption-distance and the Fermi energy are reasonably explained by analyzing the quasi-diabatic energy levels based on the local picture of adsorption.

Open-boundary cluster model for calculation of adsorbate-surface electronic states

We have developed a simple embedded-cluster model approach to investigate adsorbate-surface systems. In our approach, the physically relevant subsystem is described as an open-quantum system by considering a model cluster subject to an outgoing-wave boundary condition at the edge. This open-boundary cluster model (OCM) is free from artificial waves reflected at the cluster edge, and thus the adsorbate properties computed with the OCM are almost independent of the model cluster size. The exact continuous density of states (DOS) of a one-dimensional periodic potential model is shown to be precisely reproduced with the OCM. The accurate DOS leads to an appropriate description of adsorbate-surface chemical bonding. Moreover, the open-boundary treatment of the OCM allows us to evaluate the electron-transfer rate from the adsorbate to the surface, whereas the conventional cluster model does not give any information about such a dynamical process.

Numerically exact description of multicluster bound states

We present the variational few-body approach to multiparticle bound states called the correlated-Gaussian stochastic variational method (CGSVM) and show how it can be applied to systems of nuclear clusters. It will be demonstrated that the treatment of the intercluster motion is numerically exact and the method provides a virtually perfect realization of the conventional cluster model.

Dipped adcluster model study for molecular and dissociative chemisorptions of O2 on Ag surface

Chemisorption of an O2 molecule on a Ag surface is studied theoretically with the use of the dipped adcluster model (DAM). Electron correlations in low-lying surface states and electron-transferred states from bulk metal, which are shown to be very important, are described by the symmetry adapted cluster (SAC)/SAC-configuration interaction (SAC-CI) method. Side-on geometries are used, different from the (bent) end-on geometries studied previously. Potential curves for the O2 approaching and dissociating processes are investigated with the use of Ag2O2 and Ag4O2 adclusters. For the occurrence of chemisorption, the electron transfer from bulk metal to the adcluster, and the electrostatic image force are important, which cannot be treated by the conventional cluster model. Two different molecular adsorption states are obtained from the calculations for the Ag2O2 adcluster, namely superoxide (O2−) and peroxide (O22−) species and the corresponding adsorption energies are calculated to be 5.5 and 17.8 kcal/mol, respectively, which compare well with the experimental value 9.2–9.3 kcal/mol. The O–O stretching frequencies of these species are in good agreement with the experimental values. From the calculations for the Ag4O2 adcluster, the potential minima corresponding not only to the molecular adsorption, but also to the dissociative adsorption are obtained. The dissociative adsorption is shown to be led from the peroxide. The geometry of the dissociative O− is at the bridge site on a silver surface and the calculated Ag–O bond distance of 2.16 Å agrees well with the experimental value 2.06–2.17 Å. The dissociative adsorption energy is estimated to be 44.0–61.4 kcal/mol, which is compared with the experimental value 40.8–44.0 kcal/mol.

Theoretical study on molecular and dissociative chemisorptions of an O2 molecule on an Ag surface: dipped adcluster model combined with symmetry-adapted cluster-configuration interaction method

Chemisorption of an oxygen molecule on a silver surface is studied theoretically with the use of the dipped adcluster model (DAM) for AgxO2 with x=2 and 4. Electron correlation in low-lying surface states and electron transfer from bulk metal are described by combining DAM with the symmetry-adapted cluster (SAC) CI method. For chemisorption, electron transfer from the bulk metal to the adcluster and the electrostatic image force are important. They cannot be treated by the conventional cluster model, but are dealt with by the DAM. Three low-lying states, 2A1, 2A2, and 2B1, of the adclusters Ag2O−2 and Ag4O−2 are involved in the chemisorption. In the molecular adsorption state, the 2A1 state is assigned to peroxide (O2−2) species and the 2A2 and 2B1 states to superoxide (O−2) species. The OO stretching frequencies are in agreement with the experimental values. In the potential energy curves of Ag4O−2, another potential minimum corresponding to the dissociative adsorption state is obtained for the 2A1 state. The energetics of the molecular and dissociative adsorptions show reasonable agreement with experiments.