Functional Calculations Research Articles

Adaptive Variational Quantum Computing Approaches for Green's Functions and Nonlinear Susceptibilities.

We present and benchmark quantum computing approaches for calculating real-time single-particle Green's functions and nonlinear susceptibilities of Hamiltonian systems. The approaches leverage adaptive variational quantum algorithms for state preparation and propagation. Using automatically generated compact circuits, the dynamical evolution is performed over sufficiently long times to achieve adequate frequency resolution of the response functions. We showcase accurate Green's function calculations using a statevector simulator on classical hardware for Fermi-Hubbard chains of 4 and 6 sites, with maximal ansatz circuit depths of 65 and 424 layers, respectively, and for the molecule LiH with a maximal ansatz circuit depth of 81 layers. Additionally, we consider an antiferromagnetic quantum spin-1 model that incorporates the Dzyaloshinskii-Moriya interaction to illustrate calculations of the third-order nonlinear susceptibilities, which can be measured in two-dimensional coherent spectroscopy experiments. These results demonstrate that real-time approaches using adaptive parametrized circuits to evaluate linear and nonlinear response functions can be feasible with near-term quantum processors.

Two-dimensional XYN3 (X=V, Nb, Ta; Y=Si, Ge): Promising optoelectronic materials in photovoltaic photodetectors

Two-dimensional p-type/intrinsic/n-type (p-i-n) homojunction opens up exciting opportunities for the advancement of next-generation electronic and optoelectronic devices. However, it is urgent to explore superior two-dimensional materials for p-i-n homojunction to enhance optoelectronic performance. Herein, the electronic structures, optical properties of monolayer XYN3 (X=V, Nb, Ta; Y=Si, Ge), and the related p-i-n homojunctions are constructed and investigated systematically based on the framework of density function theory and non-equilibrium Green's function calculations. The electronic structures and optical absorption of these stable monolayers reveal that they show semiconductor characteristic with indirect bandgaps of 1.23∼2.13 eV, which possess strong absorption of visible light. The simulations of the p-i-n homojunctions based on these monolayers highlight that VSiN3 and TaSiN3-based p-i-n junctions possess maximum photocurrent densities of 21.43 and 18.48 A/m2, respectively. Moreover, the photoresponses of VSiN3 and TaSiN3-based p-i-n junctions can reach up to 0.61 and 0.55 A/W, respectively, demonstrating that VSiN3 and TaSiN3-based p-i-n junctions could be the ideal candidates for optoelectronic devices. Our work is expected to pave the way for the realization of 2D p-i-n homojunction optoelectronic devices.

Defect-Induced Sensitivity Improvement in HfNBr Monolayers for Ammonia Detection.

Two-dimensional materials, owing to their unique physical properties and high surface area, play a crucial role in intelligent sensing, particularly in the domain of atmospheric pollutant monitoring. In this work, we have extensively investigated the gas-sensing capabilities of the HfNBr monolayer for ammonia detection by introducing point defects, utilizing density functional theory and nonequilibrium Green's function calculations. Upon the introduction of point defects, the adsorption energy of HfNBr monolayers for ammonia significantly increased (from -0.162 to -1.257 eV), indicating a markedly strengthened affinity. To further elucidate the sensing mechanism, we conducted an in-depth investigation into the charge transfer dynamics, the density of states, and the charge density difference between the adsorbent and the adsorbate. Besides, we employed the NEGF method to evaluate the changes in the current-voltage characteristics of the HfNBr monolayer before and after adsorption, which revealed a remarkable change in the apparent resistance, thereby demonstrating excellent sensitivity. The exceptional performance of the HfNBr monolayer toward NH3 demonstrates its significant value in practical applications for ammonia detection.

First-principle calculations of the electronic, vibrational, and thermodynamic properties of nitrogen-rich salt of 3,6-dinitramino-1,2,4,5-tetrazine [(NH4)2(DNAT)

Energy-containing materials such as explosives have attracted considerable interest recently. In the field of high-energy materials, tetrazine and its derivatives can largely meet the requirements of high nitrogen content and oxygen balance. Nitrogen-rich energetic salts are important research subjects. Nitrogen-rich salt of 3,6-dinitramino-1,2,4,5-tetrazine is a high-energy nitrogen-rich material, but there are few related studies. This paper systematically studies the crystal structure and electronic, vibrational, and thermodynamic properties of (NH4)2(DNAT). The lattice parameters of (NH4)2(DNAT) are observed to align well with the experimental values. The properties of electrons are analyzed by band structure and density of states (DOS). The phonon dispersion curves indicate that the compound is dynamically stable. The vibrational modes of bonds and chemical groups are described in detail, and the peaks in the Raman and infrared spectra are assigned to different vibration modes. Based on the vibration characteristics, thermodynamic properties such as enthalpy (H), Helmholtz free energy (F), entropy (S), Gibbs free energy (G), constant volume heat capacity (CV), and Debye temperature (Θ) are analyzed. This article can pave the way for subsequent work or provide data support to other researchers, promoting further research. In this study, we utilized the density functional theory (DFT) for our calculations. The exchange-correlation potential and van der Waals interactions were characterized based on the GGA-PBE + G function calculation. We obtained Brillouin zone integrals using Monkhorst-Pack k-point grids, with the k-point of the Brillouin zone set to a 2 × 2 × 2 grid. During the self-consistent field operation, we set the total energy convergence tolerance to 5 × 10-6eV per atom. The cut-off energy for the calculation was established at 830eV. Additionally, the states of H (1s1), C (2s2 2p2), N (2s2 2p3), and O (2s2 2p4) were treated as valence electrons in our study.

Photoionization of Nitrile-substituted Naphthalene and Benzene: Cation Spectroscopy, Photostability, and Implications for Photoelectric Gas Heating

We investigate the vacuum ultraviolet (VUV) photodynamics of gas phase 1- and 2-cyanonaphthalene and cyanobenzene, recently detected in the Taurus molecular cloud, by combining synchrotron radiation and a double imaging electron/ion coincidence setup. The high-resolution threshold photoelectron spectra (TPES) of all three molecules are obtained experimentally from which the adiabatic ionization energies are reported with very high accuracy, particularly for 2-cyanonaphthalene, for which no data exist at this level of precision. Theoretical calculations are performed to compare with the TPES for the ground electronic state of the cations. Furthermore, the different features observed in the extended TPES have been assigned to the different molecular orbitals with the help of the outer valence Green's function calculations. The present experiments also shed light on the kinetic energy distribution of the photoelectrons as a function of the incident photon energy, to describe their contribution to the photoelectric heating effect in the interstellar medium. In this context, we show how kinetic energy distributions can be obtained from our data for any given photon energy, such as the omnipresent Lyα line, or any given interstellar radiation field (ISRF). In addition, from the total ion yields, we estimate the photorates for a few ISRFs. Finally, we discuss the photodissociation of the two cyanonaphthalenes, quoting the activation energies of the dissociation channels with the help of Rice–Ramsperger–Kassel–Marcus modeling. It is observed that CN substitution does not cause any appreciable change to the VUV dissociative photoionization relaxation channel.

Diverse quantum interference regimes in intramolecular singlet fission chromophores with thiophene-based linkers.

An array of thiophene-based π-conjugated linkers in covalently linked pentacene dimers allow us to access diverse quantum interference (QI), modulating nonadiabatic coupling (NAC) in the singlet fission (SF) process. Simulations show that structural isomerism in terms of S atom orientation substantially alters NAC with relatively marginal impacts on energies. Extended curly arrow rules (ECARs) reveal sensitive dependence of QI on SF linker topologies and connectivity, categorizing regimes of constructive, destructive, and previously unrealized in SF research, shifted destructive QI. Drastic NAC changes in terms of S atom orientation are rationalized based on the nature of QI. Our results from nonequilibrium Green's function calculation using density functional theory corroborate the classification of QI regimes based on ECARs. Moreover, we found that the extent of charge resonance contribution in electronic states relevant to multiexciton formation and the appearance of optically allowed charge transfer excitation strongly depends on the operative QI regime. Notably, the magnitude of NAC effectively captures this influence. Our findings show that QI can rationalize and semi-quantitatively correlate with NAC for the multiexciton formation step in the SF process.

Thermoelectric Power of a Single van der Waals Interface between Carbon Nanotubes.

Control of van der Waals interfaces is crucial for fabrication of nanomaterial-based high-performance thermoelectric devices because such interfaces significantly affect the overall thermoelectric performances of the device due to their relatively high thermal resistance. Such interfaces could induce different thermoelectric power from the bulk, i.e., interfacial thermoelectric power. However, from a macroscopic point of view, a correct evaluation of the interfacial thermoelectric power is difficult owing to various interface configurations. Therefore, the study of the thermoelectric properties at a single interface is crucial to address this problem. Herein, we used in situ transmission electron microscopy and nanomanipulation to investigate the thermoelectric properties of carbon nanotubes and their interfaces. The thermoelectric power of the bridged carbon nanotubes was individually measured. The existence of the interfacial thermoelectric power was determined by systematically changing the contact size between the two parallel nanotubes. The effect of interfacial thermoelectric power was qualitatively supported by Green's function calculations. When the contact length between two parallel nanotubes was less than approximately 100 nm, the experimental results and theoretical calculations indicated that the interface significantly contributed to the total thermoelectric power. However, when the contact length was longer than approximately 200 nm, the total thermoelectric power converged to the value of a single nanotube. The findings herein provide a basis for investigating thermoelectric devices with controlled van der Waals interfaces and contribute to thermal management in nanoscale devices and electronics.

Comparative Study of 2D-Cine and 3D-wh Volumetry: Revealing Systemic Error of 2D-Cine Volumetry.

This study investigates the crucial factors influencing the end-systolic and end-diastolic volumes in MRI volumetry and their direct effects on the derived functional parameters. Through the simultaneous acquisition of 2D-cine and 3D whole-heart slices in end-diastole and end-systole, we present a novel direct comparison of the volumetric measurements from both methods. A prospective study was conducted with 18 healthy participants. Both 2D-cine and 3D whole-heart sequences were obtained. Despite the differences in the creation of 3D volumes and trigger points, the impact on the LV volume was minimal (134.9 mL ± 16.9 mL vs. 136.6 mL ± 16.6 mL, p < 0.01 for end-diastole; 50.6 mL ± 11.0 mL vs. 51.6 mL ± 11.2 mL, p = 0.03 for end-systole). In our healthy patient cohort, a systematic underestimation of the end-systolic volume resulted in a significant overestimation of the SV (5.6 mL ± 2.6 mL, p < 0.01). The functional calculations from the 3D whole-heart method proved to be highly accurate and correlated well with function measurements from the phase-contrast sequences. Our study is the first to demonstrate the superiority of 3D whole-heart volumetry over 2D-cine volumetry and sheds light on the systematic error inherent in 2D-cine measurements.

On the calculation of functionals from the solution of the linear Skorohod SDE with first-order chaos in the coefficients

This article is devoted to the precise and approximate calculation of the mathematical expectation of non-linear functionals from the solution of the linear Skorohod equation with first-order chaos in the coefficients and the initial condition. In [1–4], approximate methods for calculating the mathematical expectation of functionals from solutions of the linear Skorohod stochastic differential equation with a random initial condition and deterministic coefficient functions were proposed and investigated. This paper considers the calculation of the mathematical expectation of nonlinear functionals from the solution to the linear Skorohod equation with first-order chaos in the coefficients and the initial condition. In this case, the solution is obtained in an analytical form [5]; however, it contains an unknown random parameter, determined as the solution of an auxiliary integral stochastic equation. In this paper we investigate the cases when the solution of this integral equation is found in an explicit form and then evaluate the moments and the mathematical expectations of some types of functional from the solution of the initial Skorohod equation. The construction of approximate formulas for calculating more general nonlinear functionals from the solution is considered. Numerical examples are given to illustrate the accuracy of the obtained formulas.

Sensing of sulfur containing toxic gases with double transition metal carbide MXenes

Sensing of sulfur containing gases, such as hydrogen sulfide (H2S) and sulfur dioxide (SO2), on double transition metal carbide MXenes has been studied by means of density functional theory calculations. It is found that both H2S and SO2 strongly physisorbed on M2TiC2Tx (M = Mo, Cr; Tx = O, S, OH) monolayers. The adsorption of H2S is stronger in the case of oxygen termination, (Mo2TiC2O2, Cr2TiC2O2), whereas SO2 has stronger adsorption on sulfur terminated (Mo2TiC2S2, Cr2TiC2S2) monolayers. Binding characteristics of H2S and SO2 are further confirmed with Bader charge transfer, density of states, and charge density differences. Using a statistical thermodynamic analysis, the sensing mechanism of H2S and SO2 is studied under varied pressures and temperature conditions. By means of non-equilibrium Green's function calculations, the sensitivities of H2S and SO2 on the Mo2TiC2S2 monolayer are found to be 16.3%, 10.3%, respectively, which showed promising sensing characteristics. Our results reveal that double transition metal carbide MXenes can be a potential candidate for the sensing of sulfur containing gases.

Origin and Quantitative Description of the NESSIAS Effect at Si Nanostructures

AbstractThe electronic structure of SiO2‐ versus Si3N4‐coated low nanoscale intrinsic silicon (Si) shifts away from versus toward the vacuum level Evac, originating from the Nanoscale Electronic Structure Shift Induced by Anions at Surfaces (NESSIAS). Using the quantum chemical properties of the elements involved to explain NESSIAS, an analytic parameter Λ is derived to predict the highest occupied energy level of Si nanocrystals (NCs) as verified by various hybrid‐density functional calculations and NC sizes. First experimental data of Si nanowells (NWells) embedded in SiO2 versus Si3N4 were measured by X‐ray absorption spectroscopy in total fluorescence yield mode (XAS‐TFY), complemented by ultraviolet photoelectron spectroscopy (UPS), characterizing their conduction band and valence band edge energies EC and EV, respectively. Scanning the valence band sub‐structure over NWell thickness yields an accurate estimate of EV shifted purely by spatial confinement, and thus the actual EV shift due to NESSIAS. Offsets of ΔEC = 0.56 eV and ΔEV = 0.89 eV were obtained for 1.9 nm thick NWells in SiO2 versus Si3N4, demonstrating an intrinsic Si type II homojunction. This p/n junction generated by NESSIAS eliminates any deteriorating impact of impurity dopants, offering undoped ultrasmall Si electronic devices with much reduced physical gate lengths and CMOS‐compatible materials.

Spintronic action of Cn-C6H6-Fe-C6H6-C13-n; n = 6: How crucial are d electrons?

The pi stacked complex C6C6H6-Fe-C6H6C7, while sandwiched amongst two Fe (100) electrodes display molecular spintronic characteristics with spin filtration and spin rectification under applied bias. Spintronic feature of C6C6H6-Fe-C6H6C7 has been validated by performing best in class nonequilibrium Green's function calculations and an examination of density of states of iron and carbon. Our study also reports spin filtration, spin rectification and measurement of pure spin current corresponding to n = 6. Entire explanation has been provided through a prognosis of projected device density of states and transmission pathways of our chosen system. These observations, certainly provides a new dimension in the design of pi stacked transition metal complex exhibiting spintronic feature and opens up another prospective area of spintronic research. Our study reveals that final transmission behaviour is decided by dominant carbon 2p electrons along with small contribution of 3d electrons of iron.

Proof of concept: Comparative accuracy of semiautomated VR modeling for volumetric analysis of the heart ventricles

IntroductionSimpson's rule is generally used to estimate cardiac volumes. By contrast, modern methods such as Virtual Reality (VR) utilize mesh modeling to present the object's surface spatial structure, thus enabling intricate volumetric calculations. In this study, two types of semiautomated VR models for cardiac volumetric analysis were compared to the standard Philips dedicated cardiac imaging platform (PDP) which is based on Simpson's rule calculations. MethodsThis retrospective report examined the cardiac computed tomography angiography (CCTA) of twenty patients with atrial fibrillation obtained prior to a left atrial appendage occlusion procedure. We employed two VR models to evaluate each CCTA and compared them to the PDP: a VR model with Philips-similar segmentations (VR-PS) that included the trabeculae and the papillary muscles within the luminal volume, and a VR model that only included the inner blood pool (VR-IBP). ResultsComparison of the VR-PS and the PDP left ventricle (LV) volumes demonstrated excellent correlation with a ρc of 0.983 (95% CI 0.96, 0.99), and a small mean difference and range. The calculated volumes of the right ventricle (RV) had a somewhat lower correlation of 0.89 (95% CI 0.781, 0.95), a small mean difference, and a broader range. The VR-IBP chamber size estimations were significantly smaller than the estimates based on the PDP. DiscussionSimpson's rule and polygon summation algorithms produce similar results in normal morphological LVs. However, this correlation failed to emerge when applied to RVs and irregular chambers. ConclusionsThe findings suggest that the polygon summation method is preferable for RV and irregular LV volume and function calculations.

Prediction Model and Data Simulation of Sports Performance Based on the Artificial Intelligence Algorithm.

There is still a certain deviation between the current artificial intelligence technology and the traditional learning mode, which makes it unable to be effectively applied in teaching and learning. Therefore, an effective method needs to be proposed to use functions to predict data. Function calculation can not only solve the complex problems of data calculation process but also make the data evenly distributed to take full advantage of the capabilities of each system. In this experiment, we mainly use the control function. After substituting the data into the control function, the function will automatically classify the data. In this paper, according to the actual situation of physical education in colleges and universities, from the two aspects of artificial intelligence and comprehensive learning algorithm, to build a system which can collect and analyze the past achievements of college students' physical education performance simulation can effectively help the design of physical education curriculum. According to the distribution of experimental data, a specific conclusion can be drawn; that is, the test model we choose can calculate and measure the physical fitness level of students, but there are big differences. In contrast, our experimental method using the ensemble computing model can not only predict and analyze the physical fitness level of college students but also reduce errors and shorten the time required for the experiment.

2D topological matter from a boundary Green's functions perspective: Faddeev-LeVerrier algorithm implementation

Since the breakthrough of twistronics a plethora of topological phenomena in correlated systems has appeared. These devices can be typically analyzed in terms of lattice models using Green's function techniques. In this work we introduce a general method to obtain the boundary Green's function of such models taking advantage of the numerical Faddeev-LeVerrier algorithm to circumvent some analytical constraints of previous works. We illustrate our formalism analyzing the edge features of a Chern insulator, the Kitaev square lattice model for a topological superconductor and the Checkerboard lattice hosting topological flat bands. The efficiency and accuracy of the method is demonstrated by comparison to recursive Green's function calculations.

BICOMPLEX ANALYSIS OF INVARIENT POWER SUPPLY SYSTEMS BASED ON RENEWABLE ENERGY SOURCES

The article considers a bicomplex calculation for calculating the invariant power supply systems based on renewable energy sources. Modern energy supply systems based on renewable energy sources have non-linear systems with complex transients and possible critical and chaotic regimes. The study of structures of hypernumerical systems, their features, methods of calculation and approximation of the elementary functions of a hypercomplex variable allows to effectively apply such systems in mathematical modelling of invariant power supply systems based on renewable energy sources. In some cases, the use of hypernumerical systems makes it possible to replace the original problem with an equivalent one, that is to build a bicomplex solution model.&#x0D; The system of complex numbers was considered as the initial system. With recurrent doubling of the system, hypernumerical systems of different dimensions with different properties were obtained, which made it possible to assign different values to the products of imaginary units. It is proved that the introduction of additional conditions of commutativity and associativity, which apply to real numbers and imaginary units, allows to specify the choice of a hypernumerical system.&#x0D; In the analysis of nonstationary processes of invariant systems and the study of the possibilities of hypernumerical systems, the expediency of choosing a bicomplex calculation method in mathematical modelling of systems with multiple modulation is substantiated. The method of bicomplex representation involves direct and inverse bicomplex transformation, which allows obtaining an analytically complete solution for the analysis of an invariant power supply system based on renewable energy sources. Examples of the use of bicomplex integral transformation for the analysis of systems with multiple modulation are considered. The application of the hypercomplex calculus apparatus for the transformation of systems of differential equations is proposed to simplify or compress them into one equation. It is shown that the use of hypercomplex calculus allows to significantly reduce the amount of processed information without reducing the informativeness of the mathematical model.&#x0D; The proposed formulation of tasks in a hypercomplex view allowed to compress the processing information and obtain a compact vortex for the output signal.

EVALUATION OF 67Ga CROSS SECTIONS USING EXIFON CODE FOR MEDICAL APPLICATIONS

Radioisotopes play very important roles in nuclear medicine for imaging and therapeutic applications. In the present studies, model calculation of excitation function for production of 67Ga radioisotope was performed using the EXIFON code, a nuclear reaction cross sections theoretical model code, for the reaction 65Cu(α, 2n)67Ga. The work was performed in the incident alpha energy range of 0 - 40 MeV. Similarly, the Q-value software (interface) was used for the calculation of reaction threshold and Q-value energies of the reaction of interest and were respectively found to be 14.97 MeV and -14.10 MeV. The calculated excitation function has a peak value of 1025 mb around 25 MeV incident energy. The results from the EXIFON code were compared with the experimentally measured cross sections data retrieved from IAEA database, the EXFOR database, as well as the theoretical data from Talys code via its library, the TENDL-2019. Our results partially agree with the theoretical data from Talys code (via the TENDL-2019 library) within the investigated energy region. The results however overestimated the measured (experimental) data and only agree in shape of the excitation function. The present work does not consider the effect of shell structure during the execution of the EXIFON model code. This work could be of importance to the developers and users of nuclear reaction model codes for new developments and enhancements of the existing codes, as well as to serve as a rough guide for experimentalists during production of radioisotopes for nuclear medicine applications

Devising a method for segmenting camouflaged military equipment on images from space surveillance systems using a genetic algorithm

The object of this research is the process of segmentation of camouflaged military equipment in images from space surveillance systems. The method of segmentation of camouflaged military equipment in images from space surveillance systems has been improved using a genetic algorithm. Unlike known methods, the method of segmentation of camouflaged military equipment using a genetic algorithm involves the following: – highlighting brightness channels in the Red-Green-Blue color space; – the use of a genetic algorithm in the image in each channel of brightness of the RGB color space; – image segmentation is reduced to the formation of generations and populations of chromosomes, the calculation of the objective function, selection, crossing, mutation, and decoding of chromosomes in each brightness channel of the Red-Green-Blue color space. Experimental studies were conducted on the segmentation of camouflaged military equipment using a genetic algorithm. It is established that the improved method of segmentation using a genetic algorithm makes it possible to segment images from space surveillance systems. A comparison of the quality of segmentation was carried out. It is established that the improved method of segmentation using a genetic algorithm reduces segmentation errors in the following way: – compared to the known k-means method, by an average of 15 % of errors of the first kind and an average of 7 % of errors of the second kind; – compared to the method of segmentation based on the algorithm of swarm of particles, by an average of 3.8 % of errors of the first kind and an average of 2.9 % of errors of the second kind. The improved segmentation method using a genetic algorithm can be implemented in software and hardware imaging systems from space surveillance systems

Simulation of a double-circuit subordinated coordinate regulation system of the active po wer factor corrector for the electric locomotive auxiliary electric drive

Introduction. The object of this study is an auxiliary frequency-controlled electric drive of an AC locomotive, or more specifically, the structure and parameters of the system for regulating the coordinates of the active power factor corrector, which is a part of the electric drive and a unit that ensures the energy efficiency of the electric drive as well as its electromagnetic compatibility with other equipment on board the electric locomotive and the power network. The purpose of the study is to substantiate the structure of the system for regulating the coordinates of an active power factor corrector, the choice of types of regulators and the calculation of their parameters.Materials and methods. The author has chosen as the research method the calculation of transfer functions of regulators of the subordinated regulation system, followed by computer simulation of the processes in electrical circuits using the OrCAD computer-aided design system.Results. The author made a conclusion about the expediency of using a two-circuit system of subordinated coordinate regulation containing a voltage control circuit and a current control circuit. The researcher presented and analytically compares the results of modelling of a two-circuit coordinate regulation system for the active power factor corrector for various types of regulators. The models with an aperiodic current regulator and a proportional-integral voltage regulator showed the best results.Discussion and conclusion. The obtained data serve as the basis for further improvement of the active power factor corrector operation by improving and optimising the settings, structure and algorithms of the control system, which, with the selected hardware components of the power unit, will enable it to perform its functions with a high degree of reliability in the entire range of disturbing and controlling actions on board of an electric locomotive.

Electronic Processes at the Carbon-Covered (100) Collector Tungsten Surface.

We have performed density functional VASP calculations of a pure and of a carbon-covered (100) tungsten surface under the presence of an electric field E directed away from the surface. Our aim is to answer the question of an increased penetrability of electrons at the collector side of a nanometric tunnel diode when covered by carbon atoms, a purely quantum mechanical effect related to the value of the workfunction Φ. To obtain Φ at a non-zero electric field we have extrapolated back to the electrical surface the straight line representing the linear increase in the potential energy with distance outside the metal-vacuum interface. We have found that under the presence of E the workfunction Φ = Evac − EF of the (100) pure tungsten surface has a minor dependence on E. However, the carbon-covered tungsten (100) surface workfunction Φ(C − W) has a stronger E dependence. Φ(C − W) decreases continuously with the electric field. This decrease is ΔΦ = 0.08 eV when E = 1 V/nm. This ΔΦ is explained by our calculated changes with electric field of the electronic density of both pure and carbon-covered tungsten. The observed phenomena may be relevant to other surfaces of carbon-covered tungsten and may explain the reported collector dependence of current in Scanning Field Emission Microscopy.