NH3 Molecules Research Articles

Effect of oxygen on ammonia sensing of large area graphene

Adsorption and desorption of NH3 molecules on graphene.

Adsorption and dehydrogenation of ammonia on Ru55, Cu55 and Ru@Cu54 nanoclusters: role of single atom alloy catalyst.

Hydrogen production by the catalytic decomposition of ammonia (NH3) is an important process for several important applications, which include energy production and environment-related issues. The role of single Ru-atom substitution in a Cu55 nanocluster (NC) has been illustrated using the NH3 decomposition reaction as a model system. The structural stability of Ru@Cu54 NC has been evaluated using Ru55 and Cu55 NCs for comparison. Ru@Cu54 prefers an icosahedron structure (Ih), like Ru55 and Cu55 NCs, with almost comparable average binding energies of -5.55 eV per atom. The adsorption of NHx (x = 0-3) on different adsorption sites of the icosahedron Ru@Cu54 NC has also been studied and the corresponding adsorption energies have been estimated. The site-preference investigation suggested that NH3 prefers to adsorb vertically to the Ru@Cu54. The stable geometries of the N and H atoms on the high symmetry adsorption sites of Ru@Cu54 NC have been studied. Although the N atom favours top and hollow sites, the H atom prefers to stay in the Ru-Cu bridge site along with the hollow sites. The adsorption energy of N on the Ru@Cu54 NC fcc site is found to be -5.42 eV, which is very close to the optimal value (-5.81 eV) of the ammonia decomposition volcano curve. The reaction energies for stepwise H atom elimination from an adsorbed NH3 molecule have been estimated. Finally, NH3 adsorption and decomposition on Ru@Cu54 have been illustrated in terms of electronic structure analysis. The energetics calculations for the dehydrogenation of NH3 suggest that Ru@Cu54 NC can be a suitable catalyst.

In Situ S-Doping Engineering for Highly Efficient NH3-SCR over Metal-Free Carbon Catalysts: A Novel Synergetic Promotional Mechanism.

Cyclic desulfurization-regeneration-denitrification based on metal-free carbon materials is one of the most promising ways to remove NOx and SO2 simultaneously. However, the impact of S-doping induced by the cyclic desulfurization and regeneration (C-S-R) process on the selective catalytic reduction (SCR) is not well understood. Herein, it is demonstrated that the C-S-R process at 500 °C induces in situ S-doping with a significant accumulation of C-S-C structures. NOx conversion was dramatically enhanced from 18.95% of the original sample to 84.55% of the S-doped sample. Density functional theory calculations revealed that the C-S-C structure significantly regulates the electronic structure of the C atom adjacent to the ketonic carbonyl group, thereby significantly altering the NH3 adsorption configuration with superior adsorption capacity. Moreover, S-doping induces an extra electron transfer between the N atom of the NH3 molecule and the C atom of the carbon plane, thereby promoting the activation of NH3 over the ketonic carbonyl group with a reduced energy barrier. This study elucidates a synergetic promotional mechanism between the ketonic carbonyl group and the C-S-C structure for SCR, offering a novel design strategy for high-performance heteroatom-doped carbon catalysts in industrial applications.

A New Method for Urea Synthesis under Environmental Conditions Based on Nucleophilic Addition Reaction During Electrochemical CO2 Reduction

AbstractUrea (H2NCONH2) is a commercially indispensable chemical as a fertilizer and starting material for the manufacture of many other products. Currently, commercial urea can be prepared with an energy‐consuming process by combining liquid ammonia (NH3) and liquid carbon dioxide (CO2) under high‐temperature and high‐pressure conditions. An alternative approach for synthesis of urea may involve electrochemical synthesis reactions that occur under aqueous and ambient conditions. Here, we propose synthesis of urea via nucleophilic addition reaction during an electrochemical CO2 reduction process in NH4HCO3‐containing electrolytes. The urea formation at a rate of 0.11 mmol g−1 h−1 was achieved on a polycrystalline Au electrode (area: 1 cm2) at a potential of −1.4 V (vs. saturated calomel electrode). Furthermore, the detailed investigations including in‐situ spectroscopic analysis and isotopic labeling characterization reveal the capability of producing urea could be mainly attributed to a spontaneous reaction between the NH3 molecule and the CO2⋅− intermediate. This study promotes the exploration of electrochemical synthesis of high‐value‐added products.

(Invited, Digital Presentation) Langmuir-Type Formulation for Atomic-Order Surface Reactions of Reactant Gases on Si (100) and Ge (100) Surfaces

Accurate knowledge of atomically controlled processing for group IV semiconductors is very important for the fabrication of Si-based ultrasmall devices in ultralarge-scale integration [1]. In this review, the Langmuir-type formulation is performed for atomic-order surface reactions of reactant gases on group IV semiconductor (100) surface in ultraclean hot-wall low-pressure CVD. Now, assuming that one reactant molecule M is adsorbed at one free surface site with partial decomposition of M, total site density n0 on the surface is given by n 0 = Q s + Q Ms, (1)where Q s is density of free site; Q Ms, the site density where M is adsorbed.Then the surface adsorption velocity of Q Ms is given bydQ Ms/dt = k Ms P M Q s - k -Ms Q Ms = k Ms P M n 0 - (k Ms P M + k -M) Q Ms, (2)where k Ms and k -Ms is adsorption and desorption rate constants of M, respectively; P M, partial pressure of M. The integration of eq. (2) with Q Ms = 0 at t =0 gives Q Ms= [k Ms P M n 0/(k Ms P M + k -Ms)]{1 - exp[ - (k Ms P M + k -Ms)t]}. (3)The self-limited adsorption given by eq. (3) with fitted n 0 and k Ms (k -Ms = 0) fits the experimental data of CH4 on Si(100) at 500-600oC [2], SiH3CH3 on Si and Ge(100) at 450oC [3], B2H6 on hydrogen(H)-free Si (100) at 180oC [4], PH3 on Ge (100) at 300oC [5], SiH4 on H-free Ge (100) at 260oC [6]. It is mentioned that H-free surface is prepared by preheating at the higher temperature than around 400oC on Si (100) and 300oC on Ge (100) in Ar and at the higher temperature the self-limited amount is scarcely influenced even by H2 in the present condition. In the case of NH3 at 400oC on H-terminated Si (100) [7] and SiH4 at 260oC on H-terminated Ge (100) [6], it is proposed that the NH3 or SiH4 molecules are physically adsorbed self-limitedly at H-terminated sites. Then, total site density n H0 is given by n H0 = Q Hs + Q MHs + Q HMR, (4)where Q Hs is the site density of H-terminated site; Q HMs, the site density where M is adsorbed physically at H-terminated site; Q HMR, the site density where physically adsorbed M at H-terminated site decomposes partially. If the relationship between Q Hs and Q HMs is Q HMs=K HM Q Hs with thermal equilibrium constant K HM, the surface decomposition velocity of Q HMR is given bydQ HMR/dt = k HMR Q HMR = k HMR K HM P M(n H0 - Q HMR), (5)where k HMR is partial decomposition rate constant of adsorbed M.The integration of Eq. (5) with Q HMR = 0 at t =0 gives Q HMR=n H0(1 - exp { - [k HMR K HM P M/(1 + K HM P M)]t}). (6)The H-terminated surface is composed of H-free and H-terminated sites. For fraction x of the H-terminated sites, total site density is n 0 (1 - x) + n H0 x and the self-limited amount is given by Q Ms (1 - x) + Q HMR x.The self-limited adsorption/reaction for NH3 at 400oC on H-terminated Si (100) surface and SiH4 at 260oC on H-terminated Ge (100) surface given by eqs. (3) and (6) with x, n 0, n H0, k Ms, K HM and k HMR fits the experimental data. For the SiH4, SiH3CH3 or PH3 where total site density on the surface is equal to substrate surface atomic density n SSA, it is assumed that the site is the pair site such as Si-Si, Si-Ge or Ge-Ge pair. For CH4, B2H6 or NH3 where the total site density is equal to 2n SSA, it is proposed that the site is one bond of Si or Ge. In the PH3 on Si (100) [5], it is assumed that P atoms of maximum 2n SSA are adsorbed with self-limited reaction rate constant of PH3 at the P occupied sites where PH3 molecules have been adsorbed at Si-Si pair sites [8]. These results demonstrate that the atomic level surface reactions of reactant gases in the practical low-pressure CVD are explained based on the modified Langmuir-type model.

Theoretical Insight into the Special Synergy of Bimetallic Site in Co/MoC Catalyst to Promote N2 -to-NH3 Conversion.

The catalytic mechanisms of nitrogen reduction reaction (NRR) on the pristine and Co/α-MoC(001) surfaces were explored by density functional theory calculations. The results show that the preferred pathway is that a direct N≡N cleavage occurs first, followed by continuous hydrogenations. The production of second NH3 molecule is identified as the rate-limiting step on both systems with kinetic barriers of 1.5 and 2.0 eV, respectively, indicating that N2 -to-NH3 transformation on bimetallic surface is more likely to occur. The two components of the bimetallic center play different roles during NRR process, in which Co atom does not directly participate in the binding of intermediates, but primarily serves as a reservoir of H atoms. This special synergy makes Co/α-MoC(001) have superior activity for ammonia synthesis. The introduction of Co not only facilitates N2 dissociation, but also accelerates the migration of H atom due to the antibonding characteristic of Co-H bond. This study offers a facile strategy for the rational design and development of efficient catalysts for ammonia synthesis and other reactions involving the hydrogenation processes.

Hierarchical bimetallic metal-organic frameworks with controllable assembling sub-units and interior architectures for enhanced ammonia detection

A series of hierarchical three-dimensional (3D) manganese-cobalt BTC (Mn-Co BTC; BTC = benzene-1,3,5-tricarboxylate ) metal–organic frameworks (MOFs) with controllable sub-units and interior architectures have been synthesized at room temperature without templates, etchants, or high-pressure conditions. The assembling sub-units of the hierarchical 3D Mn-Co BTC MOFs can be controlled by tuning the Mn/Co ratio, with higher Mn content favoring one-dimensional (1D) sub-units, while higher Co content favors two-dimensional (2D) sub-units. The hierarchical hollow Mn-Co BTC spheres (M2C-BTC) exhibit a frequency change (ΔF) of 383.7 Hz to 69.5 ppm of NH3 which is ∼1.7-, 2.1-, 4.2-, and 8.3-times higher than the ΔFs of hierarchical Mn-Co BTC nanorods (M1C-BTC), hierarchical flower-like Mn-Co BTC (M0.5C-BTC), Mn-BTC nanospheres, and Co-BTC nanoplates, respectively. In addition, they exhibit low limit of detection (1.12 ppm), high selectivity (41 %) and excellent stability for NH3 sensing with a minor change of 3.1 % in the ΔF value after 5 months of testing. The superior NH3 sensing performance of the hierarchical hollow Mn-Co BTC spheres may be attributed to the hollow cavities which can enhance the adsorption rate of NH3 molecules (based on the adsorption kinetics analysis) and enable them to interact with the less accessible metallic active sites on the inner cores of this MOF. The possible sensing mechanisms include the chemisorption of NH3 molecules on unsaturated metal (Mn and Co) centers as well as the hydrogen bonding between the hydroxyl and carboxyl groups with NH3.

Cu- and Al-Decorated Monolayer TiSe2 for Enhanced Gas Detection Sensitivity: A DFT Study.

The rapid industrial development has contributed to worsening global pollution, necessitating the urgent development of highly sensitive, cost-effective, and portable gas sensors. In this work, the adsorption of CO, CO2, H2S, NH3, NO, NO2, O2, and SO2 gas molecules on pristine and Cu- and Al-decorated monolayer TiSe2 has been investigated based on first-principles calculations. First, the results of the phonon spectrum and ab initio molecular dynamics simulations demonstrated that TiSe2 is dynamically stable. In addition, compared to pristine TiSe2 (-0.029 to -0.154 eV), the adsorption energy of gas molecules (excluding CO2) significantly decreased after decorated with Cu or Al (-0.212 to -0.977 eV in Cu-decorated TiSe2, -0.438 to -2.896 eV in Al-decorated TiSe2). Among them, NH3 and NO2 have the lowest adsorption energies in Cu and Al-decorated TiSe2, respectively. Further research has shown that the decrease in adsorption energy of gas molecules is mainly due to orbital hybridization and charge transfer between decorated Cu and Al atoms and gas molecules. These findings suggest that TiSe2 decorated with Cu and Al can effectively improve its sensitivity to NH3 and NO2, respectively, making it promising in gas sensing applications.

Ammonia-induced corrosion and modification of chrysocolla surface for enhanced adsorption of sulfide species

The copper content of chrysocolla is an oxidized ore, which has high industrial value in terms of development and utilization. Flotation is generally used to recover such minerals. However, few studies have been conducted on the mechanism of ammonium enhanced flotation in the flotation process of chrysotile asbestos at the atomic level, including the enhanced sulfidation process in solution and mineral surface. This study demonstrated that the presence of NH3 only enhances the reaction between Na2S⋅9H2O and Cu ions. The formation of copper-ammonia complexes facilitated the sulfide reaction and led to the generation of more Cu-S species, which can adsorb onto the chrysocolla surface. The NH3 destroys the hydration film of the Cu6[Si6O18]6H2O (1 1 0) surface, creating favorable conditions for sulfidation. The CuS formed in catalytic sulfidation has higher stability compared with CuS formed through direct sulfidation. The NH3 molecule corrosion of the Cu6[Si6O18]6H2O (1 1 0) surface was advantageous in terms of energy, and the formation of Cu(NH3)42+ was − 539.32 kJ·mol−1. After the Cu atom ultimately lost 0.37 e electrons, the Cu-O bond broke, and Cu(NH3)42+ relaxed towards the vacuum layer, which formed a defect at the Cu6[Si6O18]6H2O (1 1 0) surface. The catalytic sulfidation path in the solution was Cu(NH3)4(OH)2 + HS− + 17 H2O + Na+ → CuS + 4NH3 + OH− + 17 H2O + Na+. The total energy of the reaction was − 0.88 kJ·mol−1, which indicated that the catalytic sulfidation reaction could spontaneously occur. The CuS generated by catalytic sulfidation was stably adsorbed to the Cu6[Si6O18]6H2O surface of defects through the formation of stable chemical bond between Cu and O. The obtained results revealed the complex interaction between ammonium and minerals, which paves the way for its efficient sulfide flotation.

Formula omitted]-[formula omitted] junction from localized doping of metal-WSe2 contact with N2H4, NH4 and BF4 molecules: A first-principles investigation

Using the density-functional theory, we investigate the possibility of obtaining a p–n junction in transition metal–semiconductor junctions. The systems consist in metal surfaces, M = Ti(0001), Co(0001), Pd(111) or Pt(111) in proximity to the semiconductor WSe2 monolayer. The latter is doped with hydrazine (N2H4), ammonium (NH4), or tetrafuoroborate (BF4). We determine for the M-WSe2 systems the binding energy, work function of metal surfaces, the Schottky barrier energy with and without molecular doping and the spin polarization. Results show a strong binding between the metal and WSe2 which implies a stable M-WSe2 contacts. The Spin-polarization in Ti-WSe2 (35%), Co-WSe2 (37,5%), Pd-WSe2 (13%) and Pt-WSe2 (-0.2%) suggest a significant metal-to-WSe2 spin injection in M-WSe2. Localization of hydrazine or ammonium on the WSe2 in M-WSe2 (M = Pd, Pt) changes its conductivity from p to n-type. The strong binding, the finite spin-injection, the change in conductivity and the reduction in Shottky barrier, raise the potential for a molecule-based p–n junction in metal-WSe2 field-effect transistor.

The Study of SCR Mechanism on LaMn1−xFexO3 Catalyst Surface Based DFT

Perovskite SCR catalysts have become a hot research topic in the field of de-NOx catalyst development. This article selects LaMnO3 with high performance as the research object, modifies the catalyst by doping some iron elements instead of manganese elements, and applies density functional theory to study its reaction mechanism, providing theoretical reference for further research on perovskite. Research has found that several main reactants such as NH3, NO, and O2 can form stable adsorption at the active site, with NO more inclined to adsorb at the nitrogen atom end at the active site. The oxidation of O2 molecules after adsorption is greater than that of the active site. The adsorption capacity of the Mn active site of the catalyst before modification on the above molecules is weaker than that of the Fe active site introduced after modification. Under both anaerobic and aerobic conditions in the SCR reaction process, NH3 molecules are first adsorbed at the active site, and then influenced by lattice oxygen under anaerobic conditions. Under aerobic conditions, they are gradually dehydrogenated and produce NH2 and NH radicals. These two radicals react with NO molecules to form intermediate products in the form of NH2NO and NHNO molecules. Due to the instability of the intermediate products, they ultimately decompose into N2 and H2O molecules. The introduction of Fe active sites can increase the generation of NH2 and NH radicals during the reaction process and simplify the reaction process between NH2 radicals and NO molecules, which will be conducive to the completion of the reaction.

Clathrating CO2 in a Supramolecular Granatohedron Cage with Noncovalent CO2-NH3 Interactions and High CO2 Capture Efficiency under Ambient Conditions.

Organic amine (R-NH2) reagents as dominant chemical sorbents for CO2 capture in industrial processes suffer from high energy compensation for regeneration. Herein, we, for the first time, report the finding of Co(III) coordinating with NH3 molecules regulating the interaction between NH3 and CO2 to electrostatic interactions instead of a chemical reaction and achieve CO2 capture under near-ambient conditions. NH3 coordinating with Co(III) significantly reduces its alkalinity and reactivity with CO2 owing to its lone-pair electron donation during coordination. Under a simple protocol, CO2 induces the crystallization of CO2@[Co(NH3)6][HSO4][SO4] clathrate into a hydrogen-bonded granatohedron cage from a cobaltic hexammine sulfate aqueous solution under a CO2 pressure of 56 and 142 kPa at 275 and 298 K, respectively, with a CO2 uptake weight content of 11.7%. We reveal that CO2 interacts with cobaltous hexammine via supramolecular interactions rather than chemical bonding. The clathrate spontaneously separates from the solution as single crystals and readily releases CO2 under ambient conditions in water for cyclic utilization without further treatment. In such a rapid supramolecular capture process, molecular recognition ensures exclusive CO2 selectivity, and soluble clathrate enables the spontaneous CO2 release at a low energy penalty, exhibiting excellent practical potential in carbon capture.

Polyimide/Ionic Liquids Hybrid Membranes with NH3-Philic Channels for Ammonia-Based CO2 Separation Processes.

An efficient separation technology involving ammonia (NH3) and carbon dioxide (CO2) is of great importance for achieving low-carbon economy, environmental protection, and resource utilization. However, directly separating NH3 and CO2 for ammonia-based CO2 capture processes is still a great challenge. Herein, we propose a new strategy for selective separation of NH3 and CO2 by functional hybrid membranes that integrate polyimide (PI) and ionic liquids (ILs). The incorporated protic IL [Bim][NTf2] is confined in the interchain segment of PI, which decreases the fractional free volume and narrows the gas transport channel, benefiting the high separation selectivity of hybrid membranes. At the same time, the confined IL also provides high NH3 affinity for transport channels, promoting NH3 selective and fast transport owing to strong hydrogen bonding interaction between [Bim][NTf2] and NH3 molecules. Thus, the optimal hybrid membrane exhibits an ultrahigh NH3/CO2 ideal selectivity of up to 159 at 30 °C without sacrificing permeability, which is 60 times higher than that of the neat PI membrane and superior to the state-of-the art reported values. Moreover, the introduction of [Bim][NTf2] also reduces the permeation active energy of NH3 and reverses the hybrid membrane toward "NH3 affinity", as understood by studying the effect of temperature. Also, NH3 molecules are much easier to transport at high temperature, showing great application potential in direct NH3/CO2 separation. Overall, this work provides a promising ultraselective membrane material for ammonia-based CO2 capture processes.

Direct Simulation Monte Carlo Modeling of Ammonia in Comet C/2014 Q2 (Lovejoy)

Ammonia (NH3), likely the most abundant nitrogen-bearing molecule in cometary ices followed by hydrogen cyanide, is believed to be stored in the nucleus predominantly as a parent ice. However, spatial profiles of NH3 observed in comet C/2014 Q2 (Lovejoy) in the near-infrared region are consistent with a distributed source contribution (Dello Russo et al. 2022). We developed the direct simulation Monte Carlo model of ammonia in cometary coma and applied it to comet C/2014 Q2 (Lovejoy). Results suggest that NH3 molecules in the coma of C/2014 Q2 (Lovejoy) can plausibly originate from a combination of parent molecules of NH3 in the coma and a NH3 nucleus source. We demonstrate that the parents of NH3 having photodissociation lifetimes of several hundreds of seconds or longer (at 1 au from the Sun) can explain the observed spatial profile of NH3 in comet C/2014 Q2 (Lovejoy). Even though ammonia salts are possible candidates for parents of NH3, some simple ammonium salts such as NH4CN or NH4Cl may dissociate thermally within very short lifetimes after sublimation from the nucleus, so the contribution from those ammonium salts may be indistinguishable from the nucleus source. The lack of experimental data on photoprocesses for potential NH3 parent molecules prevent us from identifying the origin of NH3 in comets. Experimental and theoretical studies of photodissociation/ionization reactions of potential NH3 parent molecules by the solar UV radiation field are encouraged for the future identification of NH3 parents in comets.

Theoretical evaluation of gas sensing and capturing characteristics on the point defective diboron dinitride monolayer

Defects can significantly alter the properties of 2D material surfaces, thereby affecting the application results. In this work, the adsorption behaviors of H2S, SO2, NH3, and NO2 gas molecules on rationally defective diboron dinitride (n-BN) monolayers in the presence and absence of an external electric field and moisture condition are studied by the first-principles calculation approach. The results demonstrate that the boron and nitrogen defects are more likely to be generated and both defective monolayers have strong absorption effects on SO2 and NO2 gas molecules with absolute values of adsorption energy above 2.5 eV. And the conductivity change after adsorption of NO2 molecule is particularly pronounced in nitrogen defect monolayer, thus greatly increasing the sensitivity to the gas molecule. Based on the high sensitivity, the defective monolayer could be an ideal one-time scavenger for SO2 and NO2 gas molecules. While the H2S and NH3 molecules could obtain the appropriate adsorption energy and the adjustable recovery time on the defective monolayer under the dry or existent external electric field environment. These results make it possible to design a useable gas device with good gas sensing and capturing characteristics on the defective n-BN monolayer.

Numerical investigation of the hybrid pulse–DC plasma assisted ignition and NO[formula omitted] emission of NH[formula omitted]/N[formula omitted]/O[formula omitted] mixture

The ignition delay and NO emission characteristics of the NH3/N2/O2 mixture under the influence of pulse–DC hybrid plasma discharges have been studied. The plasma and combustion chemistry mechanisms for NH3/N2/O2 mixture are reviewed, an improved kinetics mechanism is proposed with a well validated electron scattering cross section data. An improved coupled plasma and combustion chemistry code allowing sensitivity/pathway analysis is developed. The role of key species on the ignition delay time and the effects of low E/N discharge over long periods of time (DC stage) on NOx emission are studied. The results show that, NO emission will be strongly enhanced due to the increased HNO, NH and N density in NH3 containing mixtures in the DC stage, NO density increases with the E/N value in DC stage due to the reduction of NH and NH2 species. The role of O2(a1Δg) in promoting ignition was studied using different rate constant of O2(a1Δg)+NO→O2+NO: O2(a1Δg) mainly reacts with H2 and H to produce radicals such as O, H and OH instead of quenched by NO. The vibrationally excited NH3(v2) molecule plays the dominating role in heat release through V–T relaxation with NH3.

Investigating the adsorption, electronic properties, and gas-sensing responses of NH3 on the B3S monolayer

Finding a suitable sensing material for NH3 has been considered to be scientifically important. In order to thoroughly understand the possibility of using a B3S monolayer (B3SML) as a sensor for detecting NH3, the adsorption behaviors, optical, gas sensing and electronic attributes of NH3 and other gas molecules were inspected on the B3SML by performing DFT calculations. Based on the results, the gas sensing performance of the pristine B3SML in detecting NH3 was good. Also, the results on the adsorption behaviors (adsorption modes, geometric structures and adsorption energies), optical/electronic attributes, electron density differences and charge transfer indicated the potential application of the B3SML as a NH3 sensor. Overall, the B3SML can be regarded as an ideal sensing material to detect NH3. The current work can provide insights into the interactions between gases and surfaces, which can be conducive to developing two-dimensional materials for detecting NH3.

Accurate and efficient calculations of Hellmann-Feynman forces for quantum computation.

First-order derivatives of energies with respect to atomic coordinates are widely computed and used in quantum chemistry simulations. The rapidly emerging technology of quantum computing offers a new paradigm for solving relevant quantum chemistry equations. In this work, we have achieved analytical calculations of atomic forces based on the Hellmann-Feynman theorem within the framework of the variational quantum eigensolver. The accuracy of the approach is demonstrated by calculating the atomic forces of H2, LiH, H2O, and NH3 molecules, which are in excellent agreement with values obtained from full configuration interaction calculations. In particular, for systems with degenerate molecular orbitals, the analytical approach has a significant accuracy advantage over finite-difference-based methods and will not involve additional computational effort on a quantum computer. The calculated forces are further used to optimize the geometries of NH3 and CH4 molecules and to perform abinitio molecular dynamics simulations for the umbrella inversion of NH3, demonstrating the feasibility of the approach in practical quantum chemistry simulations.

A numerical-tensorial "hybrid" nuclear motion Hamiltonian and dipole moment operator for spectra calculation of polyatomic nonrigid molecules.

The analysis and modeling of high-resolution spectra of nonrigid molecules require a specific Hamiltonian and group-theoretical formulation that differs significantly from that of more familiar rigid systems. Within the framework of Hougen-Bunker-Johns (HBJ) theory, this paper is devoted to the construction of a nonrigid Hamiltonian based on a suitable combination of numerical calculations for the nonrigid part in conjunction with the irreducible tensor operator method for the rigid part. For the first time, a variational calculation from abinitio potential energy surfaces is performed using the HBJ kinetic energy operator built from vibrational, large-amplitude motion, and rotational tensor operators expressed in terms of curvilinear and normal coordinates. Group theory for nonrigid molecules plays a central role in the characterization of the overall tunneling splittings and is discussed in the present approach. The construction of the dipole moment operator is also examined. Validation tests consisting of a careful convergence study of the energy levels as well as a comparison of results obtained from independent computer codes are given for the nonrigid molecules CH2, CH3, NH3, and H2O2. This work paves the way for the modeling of high-resolution spectra of larger nonrigid systems.

Analytic modelling of quantum capacitance and carrier concentration for [formula omitted]-borophene FET based gas sensor

In this work, we investigate the physical and electronic properties of β12 - borophene FET-based gas sensor using a theoretical quantum capacitance model based on tight-binding approach. We study the impact of adsorbed NH3, NO, NO2 and CO gas molecule on its density of states, carrier concentration, quantum capacitance and I–V characteristics. We found a remarkable variation in the energy band structure and the density of states (DOS) of the β12 - borophene in the presence of the adsorbed gas molecule. The appearance of non-identical Van-Hove singularities in the DOS in the presence of adsorbed gas molecules strongly indicates the high sensitivity of β12 - borophene. We found a significant increase in the carrier concentration for NH3 gas while it decreases for all other gases. Moreover, a drastic change in quantum capacitance and current–voltage relation is also observed in adsorbed gases. The different properties of the given gas molecules are compared with the pristine borophene and found to exhibit distinct wrinkles in each case, thereby indicating the strong selectivity of our proposed gas sensor. Though β12 - borophene is found to be highly sensitive for all studied gases, the NO gas is found to be most sensitive compared to the others.