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Computational quantum chemistry promises to help guide the design of catalysts that are more sustainable and economical. This Feature Article gives a tutorial overview of how our group accounts for...

We report the structural evolutions of water networks and solvatochromic response of the CH

Using a single substrate, we demonstrate a simple two-dimensional (2-D) phase grating cell with an octothorp electrode. Owing to the large spatial phase difference in any direction, the proposed grating cell has a high haze value in the opaque state (76.7%); Moreover, it has the advantages of a one-dimensional (1-D) phase grating cell, such as high fabricability, fast response time, and low operating voltage. Furthermore, the proposed grating cell has a faster response time than the 2-D grating cell (comparable to a 1-D grating cell). Consequently, we expect our proposed grating cell to find applications in virtual reality (VR)/augmented reality (AR) systems or window displays with fast response times.

A vertically aligned dichroic dye (VA-Dye) film, whose absorption axis is perpendicular to that of its substrates, was laminated on a display panel in which the absorption axis of the top polarizer was set to 0°. In the vertical viewing angle of the display panel, the absorption axes of the top polarizer and dichroic dye are at right angles to each other, and, so, the light emitted from the display panel can be blocked. In the horizontal viewing angle of the display panel, the absorption axes of the top polarizer and dichroic dye are parallel to each other so that the light emitted from the display panel can be transmitted. Based on these polarization optics, we achieved complete elimination of light emitted in the upward or downward direction of the display panel, while the light emitted to the left and right is transmitted. We also added a designed optical compensation film using a positive biaxial ( + B ) retarder to the VA-Dye film so that the light emitted in the upward and downward directions of the display panel could be blocked in a wide viewing angle range (not only in the vertical direction, but also in the diagonal direction). The display panel using the VA-Dye film with the + B retarder showed excellent optical performance, such as significantly lower transmittance over a wide viewing angle range in the upward direction and relatively higher transmittance compared to that of a reference panel without the VA-Dye film. In addition, the VA-Dye film can be manufactured with a lower thickness, easier fabrication, and lower cost when compared with other technologies.

A dye-doped LC/polymer light shutter with a polymer structure that is formed using the thermally-induced phase separation (TIPS) method is demonstrated. The TIPS method does not include any chemical reaction, and thus there is no degradation of the dye during the fabrication process. The light shutter can be fabricated quickly because the optical performance is not affected by the cooling time. The fabricated TIPS cell exhibits excellent optical performance, such as a low haze value of 0.5% in the initial transparent state, and a high haze value of 99.1% in the opaque state with a superior black color. This approach can be used for the high image quality of see-through displays using organic light-emitting diodes.

Phase change random access memory with ovonic threshold switch (OTS-PRAM) has been recently highlighted as an alternative to dynamic random access memory to meet the demand for memory capacity expansion in multicore processing. However, read disturb with inrush current (RDI) occurs owing to the snapback phenomenon caused by the threshold switching of the OTS selector in the OTS-PRAM cell, which should be resolved for realizing the practical use of OTS-PRAM. In this study, the RDI is analyzed in detail for the first time. Based on this analysis, a novel thermoelectric cooling read technique (TCR) that utilizes the thermoelectric effect in the storage material of the OTS-PRAM is proposed for effectively resolving the RDI issue. The proposed TCR is verified using the Sentaurus TCAD simulator, and a core structure with the proposed TCR is evaluated. HSPICE simulation results with a memory industry-compatible 0.25- μ m core circuit design rule for 20-nm PRAM technology show that the proposed TCR has a power gain of 67%, system performance improvement of 13.9%, and slight area overhead of 3% as compared to the SET-back write technique, which was the most promising technique for resolving the RDI issue until now.

A polarization model which accounts for electric field-induced charge transfer between fullerene molecules is introduced. Application of this model to the C60 dimer and trimer shows that intermolecular charge transfer makes a significant contribution to the polarizabilities of these clusters. This polarization model is incorporated into a one-electron Hamiltonian for describing non-valence correlation-bound anions, allowing us to further demonstrate that intermolecular charge transfer also results in increased stability of these anion states.

In this paper, we propose a new statistical corner model for the precise variation analysis of CMOS logic gate delay. The conventional corner model includes pessimism in its prediction of delay variation as a result of inadequate statistical consideration of device characteristics. Therefore, to develop an accurate delay corner model, we analytically derive corner modeling targets for device characteristics, which are statistically shrunk when considering the variation and the correlation of transistor and parasitic resistance and capacitance ( RC ). Then, the derived targets are obtained by multiplying the conventional corner parameters using the newly proposed corner scaling factors. Simulation results verify that the corner model fitted to the proposed targets accurately predicts the three standard deviation limits of delay variation. To implement the parasitic RC aware delay corner in compact models of the process design kit, an artificial neural network is used to model the complex relationship between the parasitic RC and the delay corner model. The delay variations predicted by the proposed model match well with the Monte Carlo simulation results at various simulation conditions, unlike the conventional corner model, which introduces pessimism.

Rational design of molecular chelating agents requires a detailed understanding of physicochemical ligand-metal interactions in solvent phase. Computational quantum chemistry methods should be able to provide this, but computational reports have shown poor accuracy when determining absolute binding constants for many chelating molecules. To understand why, we compare and benchmark static- and dynamics-based computational procedures for a range of monovalent and divalent cations binding to a conventional cryptand molecule: 2.2.2-cryptand ([2.2.2]). The benchmarking comparison shows that dynamics simulations using standard OPLS-AA classical potentials can reasonably predict binding constants for monovalent cations, but these procedures fail for divalent cations. We also consider computationally efficient static procedure using Kohn-Sham density functional theory (DFT) and cluster-continuum modeling that accounts for local microsolvation and pH effects. This approach accurately predicts binding energies for monovalent and divalent cations with an average error of 3.2 kcal mol-1 compared to experiment. This static procedure thus should be useful for future molecular screening efforts, and high absolute errors in the literature may be due to inadequate modeling of local solvent and pH effects.

Rational design of molecular chelating agents requires a detailed understanding of physicochemical ligand-metal interactions in solvent phase. Computational quantum chemistry methods should be able to provide this, but computational reports have shown poor accuracy when determining absolute binding constants for many chelating molecules. To understand why, we compare and benchmark static- and dynamics-based computational procedures for a range of monovalent and divalent cations binding to a conventional cryptand molecule: 2.2.2-cryptand ([2.2.2]). The benchmarking comparison shows that dynamics simulations using standard OPLS-AA classical potentials can reasonably predict binding constants for monovalent cations, but these procedures fail for divalent cations. We also consider computationally efficient static procedure using Kohn-Sham density functional theory (DFT) and cluster-continuum modeling that accounts for local microsolvation and pH effects. This approach accurately predicts binding energies for monovalent and divalent cations with an average error of 3.2 kcal mol−1 compared to experiment. This static procedure thus should be useful for future molecular screening efforts, and high absolute errors in the literature may be due to inadequate modeling of local solvent and pH effects.

We explore the kinetic processes that sustain equilibrium in a microscopic, finite system. This is accomplished by monitoring the spontaneous, time-dependent frequency evolution (the frequency autocorrelation) of a single OH oscillator, embedded in a water cluster held in a temperature-controlled ion trap. The measurements are carried out by applying two-color, infrared-infrared photodissociation mass spectrometry to the D(3)O(+)·(HDO)(D(2)O)(19) isotopologue of the “magic number” protonated water cluster, H(+)·(H(2)O)(21). The OH group can occupy any one of the five spectroscopically distinct sites in the distorted pentagonal dodecahedron cage structure. The OH frequency is observed to evolve over tens of milliseconds in the temperature range (90 to 120 K). Starting at 100 K, large “jumps” are observed between two OH frequencies separated by ∼300 cm(−1), indicating migration of the OH group from the bound OH site at 3,350 cm(−1) to the free position at 3,686 cm(−1). Increasing the temperature to 110 K leads to partial interconversion among many sites. All sites are observed to interconvert at 120 K such that the distribution of the unique OH group among them adopts the form one would expect for a canonical ensemble. The spectral dynamics displayed by the clusters thus offer an unprecedented view into the molecular-level processes that drive spectral diffusion in an extended network of water molecules.

A liquid crystal (LC) phase grating devices have been studied actively because of their outstanding features, such as the high diffraction efficiency, large diffraction angle, no diffraction at the initial state, and the simple fabrication process. It can be used to control the haze value owing to its high diffraction efficiency. Although it can be operated with low power, power consumption needs to be further reduced because it requires power to maintain the diffraction. To reduce the power consumption in a phase grating device, bistable operation, which consumes power only while it is being switched between the states, is necessary. In this paper, we will introduce bistable LC phase grating devices which can provide a translucent state with a high haze value thanks to its strong diffraction. Moreover, it can be operated with very low power as the transparent [translucent] state is maintained even after the applied vertical [in-plane] electric field is removed. We believe that these devices can be one of the new candidates for power-saving smart window or window display applications.

In this paper, we present the effects of curing temperature on switching between the transparent and translucent states in a polymer-stabilized liquid-crystal (PSLC) cell. When cured at a low temperature, polymer structures are formed without disturbing the initial alignment of LCs so that haze in the transparent state is dramatically reduced. Moreover, we can achieve very fast switching between the haze-free transparent and high-haze translucent states because there is a little degradation in the performance of the transparent and translucent states when the polymer concentration is increased. We demonstrated an ON–OFF response time of less than 3 ms and a gray-to-gray response time of less than 6 ms in a PSLC cell.

The adsorption, formation, and interaction energies between carbon dioxide (CO2) and carbon oxide functional groups on porous carbon surface were analyzed through XPS, textural analysis, CO2 gas adsorption, and theoretical study. Carbon molecular sieves (CMSs) as porous carbon were modified by several concentrations of hydrogen peroxide (H2O2) solution under atmospheric conditions in an attempt to introduce carbon oxide groups and increase their CO2 adsorption capacity. Created oxide groups on carbon surface of CMSs were determined by XPS analysis and the CO2 adsorption capacities were investigated through the CO2 adsorption isotherms at 273 and 298 K at low pressure (max. 800 mmHg). The CO2 uptake capacity on CMSs modified by H2O2 was increased compared to an unmodified CMS and increased with increasing carboxylic (-COOH) group concentration on the carbon surface of CMSs. For a theoretical approach, binding energies between CO2 and various functional groups on the surface of CMSs have been investigated using several electronic structure calculations. As the result of the computational study by the MP2 method, a carboxylic group has the highest binding energy for CO2 (-COOH····CO2) of 4.45 kcal/mol, compared to quinone (dbndO) of 3.9, phenol (-OH) of 3.2 and lactone (-O-C=O) of 3.57 kcal/mol. This work demonstrates that introducing -COOH groups on CMS by H2O2 are a suitable modification for CO2 adsorption.

We report control of the haze value in a liquid crystal (LC) cell driven by a fringe electric field. When a fringe field is applied to a vertically aligned (VA) cell, a large spatial phase differen...

In this paper, we present a diffractive liquid crystal (LC) device capable of rapid switching between the transparent and translucent states for window display applications. In contrast to previously reported LC light shutters based on light scattering, the proposed LC device relies on diffraction of white incident light by an electric field-induced periodic continuous LC profile. It can be switched between the transparent and translucent states without a complicated driving scheme or a polymer structure. This device exhibits outstanding features for window display applications, such as a high transparency and a wide viewing angle in the transparent state, a low operating voltage, and a short response time.

A static random access memory (SRAM) operational mismatch (SOMM) corner model and a methodology to efficiently estimate the SRAM read and write stability yield with the SOMM corner model are proposed. The proposed SOMM corner model effectively finds the combination of the transistor mismatch in SRAM, which represents the worst SRAM read or write operation in the given probabilistic distance (e.g., six sigma), and the SRAM yield can be estimated from the smallest probabilistic distance at which read or write operation failure occurs. With the proposed SOMM corner model implemented in the process design kit, the circuit designers can optimize the SRAM design by estimating the SRAM yield with significantly fewer computational resources, compared with the previous Monte Carlo-based methodologies. Numerical experiments show that the yield estimated by the proposed methodology matches well with the yield by Monte Carlo with importance sampling (error < 0.1 sigma); the simulation time takes less than 1 min, which is three orders of magnitude speedup over the conventional importance sampling methods.

We report a simple method for reducing the response time of homogeneously aligned liquid crystal (LC) cells by using two-dimensional confinement of the LCs. We have shown that the switching speed can be increased by serval fold in in-plane switching and fringe-field switching cells by introducing interdigitated electrodes parallel to the LC alignment direction. We also report an interdigitated pixel electrode structure with alternating tilts for a much wider viewing angle by aligning the LCs without a pretilt. In addition to a short response time and wide viewing angle, this device allows a much larger deviation of the LC alignment direction which is essential for mass production. Moreover, LCs with negative dielectric anisotropy can be used to minimize the transmittance decrease.

The effects of water vapor on the catalytic activity of a Fe-BEA catalyst in the NH 3 -SCR reaction for N 2 O and NO were investigated using diffusive reflectance infrared Fourier transform spectroscopy (DRIFTS) tests and SCC-DFTB calculation. It was found that water vapor only decreased the N 2 O conversion rate and did not affect the conversion rates of NO. The DRIFTS analysis revealed that the presence of water increased the adsorption strength of nitrous oxide (N 2 O) on the catalyst surface. On the other hand, nitric oxide (NO) conversion route was only altered from NO 2 -SCR to standard selective catalytic reduction (SCR) upon injection of water vapor. It was confirmed that the water vapor not only inhibited the desorption of N 2 O during the reduction step but also induced stronger adsorption of N 2 O during the NH 3 -SCR reaction. A computational chemical model that includes hydroxyl zeolite, N 2 O, and NO supported the experimental result showing binding force between the hydroxyl zeolite and N 2 O is much higher than that between hydroxyl zeolite and NO. It is believed that the stronger adsorption induced by water vapor caused delayed dissociation of N 2 O thereby not allowing for catalytic conversion.

Purpose To evaluate the clinical symptoms of patients with dry eyes, based on the ocular surface disease index (OSDI) and analyze the relationship between OSDI and various ocular surface parameters. Methods This was a retrospective study that included 45 eyes of 45 dry eye patients who visited the Seoul Nune Eye Hospital from August 2017 to December 2017. The patients were assessed by non-invasive keratography for the first break-up time, lipid layer thickness (LLT), tear osmolarity, tear matrix metalloproteinase-9 immunoassay as well as with the conventional Schirmer I test and fluorescein break-up time. The patient's symptoms were evaluated by the OSDI questionnaires and correlations were analyzed based on the parameters described above. Results There were significant negative correlations between OSDI and non-invasive keratography for the first break-up time (p = 0.038, r = -0.330), and LLT (p = 0.005, r = -0.426). However, there were no significant correlations between OSDI and fluorescein break-up time, Schirmer I score, and tear osmolarity (p = 0.173, 0.575, and 0.844 respectively). OSDI was not significantly different between matrix metalloproteinase-9 positive and negative groups (p = 0.768). Conclusions Non-invasive examinations such as non-invasive keratograph break-up time and interferometry of LLT can be efficient tools for evaluating dry eye symptoms.

We exploit gas-phase cluster ion techniques to provide insight into the local interactions underlying divalent metal ion-driven changes in the spectra of carboxylic acids at the air–water interface. This information clarifies the experimental findings that the CO stretching bands of long-chain acids appear at very similar energies when the head group is deprotonated by high subphase pH or exposed to relatively high concentrations of Ca 2+ metal ions. To this end, we report the evolution of the vibrational spectra of size-selected [Ca 2+ ·RCO 2 − ] + ·(H 2 O) n =0 to 12 and RCO 2 − ·(H 2 O) n =0 to 14 cluster ions toward the features observed at the air–water interface. Surprisingly, not only does stepwise hydration of the RCO 2 − anion and the [Ca 2+ ·RCO 2 − ] + contact ion pair yield solvatochromic responses in opposite directions, but in both cases, the responses of the 2 (symmetric and asymmetric stretching) CO bands to hydration are opposite to each other. The result is that both CO bands evolve toward their interfacial asymptotes from opposite directions. Simulations of the [Ca 2+ ·RCO 2 − ] + ·(H 2 O) n clusters indicate that the metal ion remains directly bound to the head group in a contact ion pair motif as the asymmetric CO stretch converges at the interfacial value by n = 12. This establishes that direct metal complexation or deprotonation can account for the interfacial behavior. We discuss these effects in the context of a model that invokes the water network-dependent local electric field along the C–C bond that connects the head group to the hydrocarbon tail as the key microscopic parameter that is correlated with the observed trends.

This paper presents a dye-doped liquid crystal (LC) phase-grating cell that is switchable between transparent, dark, and opaque states. The device can control haze and transmittance independently. Initially, LC and dye molecules are twist-aligned to make the cell opaque but haze-free due to the absorption of incident light without scattering. Switching to the transparent state could be achieved by applying a vertical electric field, whereas switching to the opaque state could be achieved by applying an in-plane electric field. It exhibited several advantages, such as a low switching voltage (

A polarization model which accounts for electric field-induced charge transfer between fullerene molecules is introduced. Application of this model to the C60 dimer and trimer shows that intermolecular charge transfer makes a significant contribution to the polarizabilities of these clusters. This polarization model is incorporated into a one-electron Hamiltonian for describing non-valence correlation-bound anions, allowing us to further demonstrate that intermolecular charge transfer also results in increased stability of these anion states.

A dye-doped LC/polymer light shutter with a polymer structure that is formed using the thermally-induced phase separation (TIPS) method is demonstrated. The TIPS method relies on the difference in solubility between thermoplastic polymer and solvent, and thus there is no degradation of the dye during the fabrication process. The light shutter can be fabricated quickly because the optical properties are not affected by the cooling time. The fabricated TIPS cell shows a superior black color with excellent optical properties, such as a low haze value of 0.5% in the transparent state, and a high haze value of 99.1% in the opaque state. This result can be applied for the high image quality of see-through displays using organic light-emitting diodes.

We propose a two-dimensional (2D) polymer-walled liquid-crystal (LC) phase-grating device, which can be used to control the haze with a very low power. 2D polymer walls can be formed in an LC cell through ultraviolet light irradiation while applying an in-plane electric field through phase separation induced by the spatial elastic energy difference. The transparent and translucent states can be realized by applying vertical and in-plane electric fields to the 2D polymer-walled LC cell, respectively. The cell can be operated with a very low power as the transparent [translucent] state is maintained even after the applied vertical [in-plane] electric field is removed. It consumes power only during state switching. The fabricated device exhibits outstanding performances, such as a very low operating voltage (10 V), low haze (2%) in the transparent state, high haze (90%) in the translucent state, and short switching time (2 ms), compared to those of other bistable LC devices, which can be used to control the haze.

The effects of the interplay between pressure and surface chemistry on the transformation of few-layer graphene into an sp 3 -bonded carbon film were investigated with first-principles density functional theory calculations including ab initio molecular dynamics. N 2 H 4 , H 2 O, and He were each considered as a candidate pressure medium. Compared with the bulk graphite, the surface chemistry overwhelmingly governed the conversion energetics for nanometer-thick graphene layers. A hydrogen-donating medium reduced the required conversion pressure compared with an inert one; the conversion pressure obtained by using N 2 H 4 was 40% of the corresponding pressure obtained with He. We suggest that pressurizing the cell through hydrogen-donating pressure media has the advantage from the surface chemistry by concentrating hydrogen atoms on carbon surfaces.

We report cell gap effects on the electro-optic characteristics of a polymer-stabilized liquid crystal (LC) cell. We found that the transmittance of a polymer-stabilized LC cell can be increased by increasing the cell gap with little increase in response time. To better understand the cell gap effect on response time of the polymer-stabilized LC cell, we employed a simple method to evaluate and predict the response time by extracting the average distance between two neighboring bundles through experiment. The experimental results related to the response time of a polymer-stabilized LC cell matche well with the calculated results. We experimentally obtained turn-off switching that was three times faster than that of a conventional fringe-field switching cell at room temperature. Even at −20 °C, we achieved a relatively fast turn-off time of 18 ms.

Low-frequency driving of a liquid crystal display (LCD) panel to minimise power consumption has drawn much attention recently. In case an LCD panel is driven by a low-frequency fringe field, image flickering phenomenon is detected by the naked human eye when the sign of the applied electric field is reversed. We investigated the effect of electrode spacing on the image flickering phenomenon induced by the flexoelectric effect in a fringe-field-switching (FFS) liquid crystal cell. We found that the image flicker in an FFS cell under low-frequency driving can be eliminated in a simple manner by changing the electrode spacing.

Proposed herein is a method of controlling the viewing angle in a hybrid-aligned liquid crystal (LC) cell using a vertical bias electric field. Using the proposed method, the viewing angle can be continuously controlled by changing the bias voltage. A vertical bias electric field is applied to the cell for a wide viewing angle whereas no bias electric field is applied for a narrow viewing angle. The proposed cell shows a submillisecond response time.