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We show that accurate exchange–correlation hybrid functionals give very physically optimized effective-correlation potentials, capable of correctly describing the quantum oscillations of atoms and molecules. Based on this analysis and on understanding the error cancellation between semilocal exchange and correlation functionals, we propose a very simple, semilocal correlation potential model compatible with the exact exchange of density functional theory, which performs remarkably well for charge densities and orbital energies.

This paper investigates reconfigurable physical unclonable function (PUF) design by exploiting the polarization switching variation and stochasticity in ferroelectric field-effect-transistors (FeFETs). The proposed PUFs include 1-transistor/cell (1T/C) and 2T/C designs. The denser 1T/C PUF splits random ‘0’ and ‘1’ states using a tactically pre-defined reference. The 2T/C PUF needs no dedicated references and obtains unbiased random states by differentiating two FeFETs under a proposed sensing error cancellation scheme. Experimental measurements have shown the uniform randomness, uniqueness, repeatability and reconfigurability of the response. Further simulations using an experimentally calibrated multi-domain FeFET model show high energy efficiency and robustness on design parameters.

Post-self-consistent dispersion corrections are now the norm when applying density-functional theory to systems where non-covalent interactions play an important role. However, there is a wide range of base functionals and dispersion corrections available from which to choose. In this work, we opine on the most desirable requirements to ensure that both the base functional and dispersion correction, individually, are as accurate as possible for non-bonded repulsion and dispersion attraction. The base functional should be dispersionless, numerically stable, and involve minimal delocalization error. Simultaneously, the dispersion correction should include finite damping, higher-order pairwise dispersion terms, and electronic many-body effects. These criteria are essential for avoiding reliance on error cancellation and obtaining correct results from correct physics.

A new physics-based uncertainty quantification methodology is developed for understanding model form uncertainty. This framework provides insights into the reasons and conditions under which model assumptions are wrong and is used to study model form uncertainty in two-equation Reynolds-Averaged Navier-Stokes turbulence models in wall-bounded flows. Through this analysis, the shortcomings of these models are understood with an emphasis on the role of anisotropy. Error cancellation is shown to largely benefit two-equation turbulence models in wall-bounded flows, leading to models that provide correct predictions but lack physical correctness.

Accelerators magnets must have minimal magnetic field imperfections to reduce particle-beam instabilities. In the case of coils made of high-temperature superconducting (HTS) tapes, the magnetization due to persistent currents adds an undesired field contribution, potentially degrading the magnetic field quality. In this paper we study the use of superconducting screens based on HTS tapes for reducing the magnetic field imperfections in accelerator magnets. The screens exploit the magnetization by persistent currents to cancel out the magnetic field error. The screens are aligned with the main field component, such that only the undesired field components are compensated. The screens are self-regulating, and do not require any externally applied source of energy. Measurements in liquid nitrogen at 77 K show for dipole-field configurations a significant reduction of the magnetic field error up to a factor of four. The residual error is explained via numerical simulations accounting for the geometric defects in the HTS screens, achieving satisfactory agreement with experimental results. Simulations show that if screens are increased in width and thickness, and operated at 4.5 K , field errors may be eliminated almost entirely for the typical excitation cycles of accelerator magnets.

We performed density-functional calculations to estimate the formation energies of intermetallic alloys. We used two semilocal approximations, the generalized gradient approximation (GGA) by Perdew-Burke-Ernzerhof (PBE), and the strongly constrained and appropriately normed (SCAN) meta-GGA. In addition, we utilized two nonlocal DFT functionals, the hybrid HSE06, and the state-of-the-art random phase approximation (RPA). The nonlocal functionals such as HSE06 and RPA yield accurate formation energies of binary alloys with completely filled $d$-band metals, where semilocal functionals underperform. The accuracy of the nonlocal functionals is greatly reduced when a partially filled $d$-band metal is present in an alloy, while PBE-GGA outperforms in these cases. We show that the accurate prediction of formation energies by any DFT method depends on its ability to predict the accurate electronic properties, e.g., valence $d$-band contribution to the density of states (DOS). The SCAN meta-GGA often corrects the PBE-DOS, however, it does not provide accurate formation energies compared to PBE. This is assumed to be due to the lack of proper error cancellation that should be expected due to the similar bulk nature of both alloys and their constituents, which may improve with the modification of meta-GGA ingredients. RPA yields too-negative formation energies of alloys with partially filled $d$-band metals. RPA results can be corrected by restoring the exchange-correlation kernel, thereby improving the short-range electron-electron correlation in metallic densities.

Recent advances in theoretical thermochemistry have allowed the study of small organic and bio-organic molecules with high accuracy. However, applications to larger molecules are still impeded by the steep scaling problem of highly accurate quantum mechanical (QM) methods, forcing the use of approximate, more cost-effective methods at a greatly reduced accuracy. One of the most successful strategies to mitigate this error is the use of systematic error-cancellation schemes, in which highly accurate QM calculations can be performed on small portions of the molecule to construct corrections to an approximate method. Herein, we build on ideas from fragmentation and error-cancellation to introduce a new family of molecular descriptors for machine learning modeled after the Connectivity-Based Hierarchy (CBH) of generalized isodesmic reaction schemes. The best performing descriptor ML(CBH-2) is constructed from fragments preserving only the immediate connectivity of all heavy (non-H) atoms of a molecule along with overlapping regions of fragments in accordance with the inclusion-exclusion principle. Our proposed approach offers a simple, chemically intuitive grouping of atoms, tuned with an optimal amount of error-cancellation, and outperforms previous structure-based descriptors using a much smaller input vector length. For a wide variety of density functionals, DFT+ΔML(CBH-2) models, trained on a set of small- to medium-sized organic HCNOSCl-containing molecules, achieved an out-of-sample MAE within 0.5 kcal/mol and 2σ (95%) confidence interval of1.5 kcal/mol compared to accurate G4 reference values at DFT cost.

Density functional theory (DFT) is used in thousands of papers each year, yet lack of universality reduces DFT’s predictive capacity, and functionals may produce energy-density imbalances. The absolute electronegativity (χ) and hardness (η) directly reflect the energy–density relationship via the chemical potential ∂E/∂N and we thus hypothesized that they probe universality. We studied χ and η for atoms Z = 1–36 using 50 diverse functionals covering all major classes. Very few functionals describe both χ and η well. η benefits from error cancellation, whereas χ is marred by error propagation from IP and EA; thus, almost all standard GGA and hybrid functionals display a plateau in the MAE at ∼0.2 eV–0.3 eV for η. In contrast, variable performance for χ indicates problems in describing the chemical potential by DFT. The accuracy and precision of a functional is far from linearly related, yet for a universal functional, we expect linearity. Popular functionals such as B3LYP, PBE, and revPBE perform poorly for both properties. Density sensitivity calculations indicate large density-derived errors as occupation of degenerate p- and d-orbitals causes “non-universality” and large dependency on exact exchange. Thus, we argue that performance for χ for the same systems is a hallmark of an important aspect of universality by probing ∂E/∂N. With this metric, B98, B97-1, PW6B95D3, MN-15, rev-TPSS, HSE06, and APFD are the most “universal” among the tested functionals. B98 and B97-1 are accurate for very diverse metal–ligand bonds, supporting that a balanced description of ∂E/∂N and ∂E2/∂N2, via χ and η, is probably a first simple probe of universality.

One of the central problems for near-term quantum devices is to understand their ultimate potential and limitations. We address this problem in terms of quantum error mitigation by introducing a framework taking into account the full expressibility of near-term devices, in which the optimal resource cost for the probabilistic error cancellation method can be formalized. We provide a general methodology for evaluating the optimal cost by connecting it to a resource-theoretic quantifier defined with respect to the noisy operations that devices can implement. We employ our methods to estimate the optimal cost in mitigating a general class of noise, where we obtain an achievable cost that has a generic advantage over previous evaluations, as well as a fundamental lower bound applicable to a broad class of noisy implementable operations. We improve our bounds for several noise models, where we give the exact optimal costs for the depolarizing and dephasing noise, precisely characterizing the overhead cost while offering an operational meaning to the resource measure in terms of error mitigation. Our result particularly implies that the heuristic approach presented by Temme et al. [K. Temme, S. Bravyi, and J. M. Gambetta, Phys. Rev. Lett. 119, 180509 (2017)] is optimal even in our extended framework, putting fundamental limitations on the advantage provided by the extra degrees of freedom inherent in near-term devices for this noise model., 5+6 pages, 1 figure; published version

The self-interaction error (SIE), i.e. unphysical interactions of electrons with themselves, has plagued developers and users of Density Functional Approximations (DFAs) since the inception of Density Functional Theory (DFT). Formally, it can be separated into the one-electron and many-electron SIE; herein we present one of the most comprehensive studies of the first. While we focus mostly on the total SIE, we also make use of two different decompositions. The first is a separation into functional and density-driven errors as championed by Sim, Burke and co-workers [J. Phys. Chem. Lett., 2018, 9, 6385–6392]; the second separates the error into exchange, correlation, and one-electron components, with the latter being a density error that has not been discussed in this form before. After investigating the familiar hydrogen atom and dihydrogen cation, we establish a relationship between the SIE and the nuclear charge with the help of a series of heavier hydrogenic analogues. For the mononuclear systems and the diatomics at the dissociation limit, this relationship is linear in nature with prominent exceptions, mostly belonging to the Minnesota and range-separated (double-)hybrid DFAs. For the first time, we also show how the magnitude of the SIE depends on the underlying atomic-orbital basis set and how DFAs that rely on a popular van-der-Waals DFT type London-dispersion term exhibit “self-dispersion”. We find that range separation is not a panacea for solving the one-electron SIE. DFAs that have been developed to be one-electron SIE free for one system, such as the hydrogen atom, show larger errors for heavier hydrogenic systems. Often, one-electron SIE-free DFAs rely on fortuitous error cancellation between their exchange and correlation components. An analysis of the most robust methods for general applications to date reveals that they suffer moderately from the one-electron SIE, while DFAs that are nearly SIE-free do not perform well in applications. Implicit in the continued existence of the one-electron SIE is that well-performing DFAs continue to suffer insufficiencies at their fundamental levels that are being compensated for by the SIE. Our analysis includes more than 250 000 datapoints, resulting in multiple insights that may drive future developments of new DFAs or SIE corrections.

We present a benchmark study on equilibrium structures optimized with subsystem density functional theory (sDFT) employing a new analytical gradient implementation in the program SERENITY. Geometry optimizations are performed on all complexes of the S22 [Jurečka et al. Phys. Chem. Chem. Phys. 2006, 8, 1985-1993] and A24 [Řezáč and Hobza. J. Chem. Theory Comput. 2013, 9, 2151-2155] test sets. While some combinations of approximate exchange-correlation (XC) and nonadditive kinetic-energy functionals (e.g., LDA/Thomas-Fermi or PW91/PW91k) more or less successfully mimic the effect of medium-range dispersion in these complexes, we also include the combination of BP86/LLP91. This functional reproduces the dispersion problem of the corresponding BP86 Kohn-Sham (KS-)DFT calculations and can hence successfully be corrected by empirical dispersion corrections developed for KS-DFT. We propose this as a robust and accurate strategy for sDFT geometry optimizations, which appears to be preferable over the previously used strategy relying on error cancellation between XC and nonadditive kinetic-energy functionals. In fact, the best results in our benchmark are obtained from BP86/LLP91 together with a D3-type dispersion correction. We also discuss the difference between our Gaussian-type orbital implementation in SERENITY and a Slater-type orbital based implementation in the Amsterdam density functional (ADF) program but only find small differences in most cases.

Molecular dynamics is expected to produce accurate results over a wide range of conditions and timescales. However, this is not always the case since the field has been too reluctant to abandon historically popular techniques known to introduce artefacts. Two recent papers have suggested there are reliability issues in the GROMACS code since it no longer uses a legacy twin-range algorithm. Here, we show there are order-of-magnitude differences in accuracy favoring the modern Trotter decomposition, and that a force field relying on the old algorithm will have errors parametrized into the force field. Similarly, the suggestions about incorrect virial calculations turn out to be explained by insufficient accuracy in the default SHAKE settings used for GROMOS, while the GROMACS default choices are accurate. This highlights the importance of being more critical to error cancellation in simulations in order for algorithms and parameters to both gradually converge to more perfect ones.

Empirical, highly accurate non-relativistic electronic total atomization energies (eTAEs) are established by combining experimental or computationally converged treatments of the nuclear motion and relativistic contributions with the total atomization energies of HF, CO, N2, and H2O obtained from the Active Thermochemical Tables. These eTAEs, which have estimated (2σ) uncertainties of less than 10 cm−1 (0.12 kJ mol−1), form the basis for an analysis of high-level ab initio quantum chemical calculations that aim at reproducing these eTAEs for the title molecules. The results are then employed to analyze the performance of the high-accuracy extrapolated ab initio thermochemistry, or High-Accuracy Extrapolated Ab Initio Thermochemistry (HEAT), family of theoretical methods. The method known as HEAT-345(Q), in particular, is found to benefit from fortuitous error cancellation between its treatment of the zero-point energy, extrapolation errors in the Hartree-Fock and coupled cluster contributions, neglect of post-(T) core-correlation, and the basis-set error involved in higher-level correlation corrections. In addition to shedding light on a longstanding curiosity of the HEAT protocol—where the cheapest HEAT-345(Q) performs comparably to the theoretically more complete HEAT-456QP procedure—this study lays the foundation for extended HEAT variants that offer substantial improvements in accuracy relative to the established approaches.

In this work we propose a cost-effective protocol for the calculation of rate constants within the framework of multiconformer transition state theory. We have developed this methodology while calculating for the first time on a theoretical level rate constants for a series of six reactions between the OH radical and hydrofluoropolyethers: the latter are promising third-generation CFC replacements whose atmospheric impact is still widely unknown. Our investigation, which is based on computationally accessible M08-HX/apcseg-2//M08-HX/pcseg-1 calculations, shows that two of our rate constants are within a factor of 0.6 and 1.4 of experimental data, a good result that probably benefits from some error cancellation. It also exhibits a reactivity trend, for which we provide detailed insights that could be used to shed new light on the general reactivity of ethers towards OH. Finally, because the studied reactions share an ubiquitous mechanism in atmospheric chemistry, we hope that our protocol can be routinely applied to explore the reactivity of computationally challenging reactions and to pave new ways in the development of greener CFC replacements.

Potential reconstruction is a powerful strategy for deriving accurate (sometimes called "exact") embedding potentials in the context of density-dependent embedding methods. It is particularly useful for partitioning covalent bonds in such fragment-based electronic-structure methods. While the general approach is well defined and easily explained, there are a number of choices to be made in practice, concerning, e.g., the specific reconstruction algorithm, the assignment of electrons to subsystems, or the initial guess potential. A general choice to be made is whether "exact" embedding potentials shall be derived for pre-defined target densities (top-down) or for approximate fragment densities that can be iteratively defined (bottom-up). Here, we compare the pros and cons of a variety of different variants of potential reconstruction, both in terms of conceptual issues and concerning their accuracy and efficiency. We also present several algorithmic improvements that can be crucial in critical cases of potential reconstruction, namely, we show (i) that a combination of basis-set and grid-based potential reconstruction schemes can lead to improved resulting densities, (ii) that similarly the combination of real-space and matrix-representation based potential reconstruction gives great advantages, and (iii) that the potential-matrix reconstruction by Zhang and Carter [J. Chem. Phys. 148, 034105 (2018)] can be made much more efficient by avoiding an explicit Hessian calculation. Additionally, we demonstrated (iv) that a double reconstruction, meaning a reconstruction of both the supersystem potential and the subsystem potential, may lead to beneficial error cancellation. We also address the question of consistent energetics derived from such reconstructed potentials.

The contact between rough surfaces with adhesion is an extremely difficult problem, and the approximation of the DMT theory (to neglect deformations due to attractive forces), originally developed for spherical contact of very small radius, are receiving some new interest. The DMT approximation leads to extremely large overestimate of the adhesive forces in the case of spherical contact, except at pull-off. For cylindrical contact, the opposite trend is found for larger contact areas. These findings suggest some caution in solving rough contacts with DMT models, unless the Tabor parameter is really low. Further approximate models like that of Pastewka & Robbins' may be explained to work only for a coincidence of error cancellation in their range of parameters., 11 pages, 5 figures

This paper presents a new dither adding method for multistage-noise-shaping (MASH) digital delta-sigma modulator (DDSM), to reduce the output spurious tones. In this method, the additive dither signal is added to two different nodes of any preceding stage of the MASH DDSM, without using dither shaping filter. Then, those dither signals are sent to the error cancellation logic (ECL), where they are eliminated by each other, avoiding appearing in the output spectrum. Simulation results show that, for the MASH DDSM, the new dither adding method can guarantee a spur-free spectrum for all digital constant inputs without raising the noise floor.

We investigated the basis set convergence of high-order coupled-cluster interaction energy contributions for 21 small weakly bound complexes. By performing CCSDT(Q) calculations in at least the aug-cc-pVTZ basis set, and CCSDT calculations in at least aug-cc-pVQZ (aug-cc-pVTZ for one system), we found the convergence to be quite slow. In particular, the 6-31G*(0.25) and 6-31G**(0.25,0.15) bases advocated by Hobza et al. (J. Chem. Theory Comput. 2013, 9, 2151; ibid. 2013, 9, 3420) are unsuitable for the post-CCSD(T) effects, with average errors for the CCSDT(Q)-CCSD(T) interaction energy contribution of about 80% for 6-31G**(0.25,0.15) and 110% for 6-31G*(0.25). Upgrading the basis set to aug-cc-pVDZ reduces the average error to about 35% and extremely demanding CCSDT(Q)/aug-cc-pVTZ calculations are necessary for further improvement in accuracy. An error cancellation between basis set incompleteness effects at the CCSDT-CCSD(T) and CCSDT(Q)-CCSDT levels occurs for most (but not all) complexes, making it unproductive to carry out CCSDT calculations in a larger basis set than the more demanding CCSDT(Q) calculations. We also found that the frozen natural orbital approximation at the CCSDT and CCSDT(Q) levels works well only if the thresholds for discarding least occupied natural orbitals are very tight (significantly tighter than the thresholds recommended for molecular correlation energies in the original work of Rolik and Kállay, J. Chem. Phys. 2011, 134, 124111), making the performance gains quite limited. The interaction energy contributions through CCSDT(Q) are both a necessity and a bottleneck in the construction of top-accuracy interaction potentials and further improvements in the efficiency of high-order coupled-cluster calculations will be of great help.

This study compares PC-SAFT and SAFT + Cubic in predicting various thermodynamic properties of 7 haloethanes. The correct estimation of the pure compound critical points contributes to a superior over-all robustness and reliability of SAFT + Cubic. However SAFT + Cubic is less accurate in modeling vapor pressures and isobaric heat capacities away from the critical points. Nevertheless, while being imprecise in predicting C P and C V separately, SAFT + Cubic establishes a more successful mutual error cancellation of these properties, both for ratio and for arithmetic average. Hence, the inaccurate estimations of heat capacities have relatively small impact on predictions of sound velocities. Considering the fact that the heat capacities in engineering equipment are somewhere between constant-volume and constant-pressure conditions, SAFT + Cubic might in fact yield reasonable estimations of the actual data. However its strongest points in comparison to PC-SAFT are the predictions of sound velocities and phase equilibria.

COSMO-RS, the Conductor-like Screening Model for Real Solvents, has been used to predict a set of basic partition coefficients of 22 (alkylated) naphthalenes. To validate the approach, methyl-, dimethyl-, and ethylnaphthalenes have been chosen, according to the availability of experimental data. Then, predictions have been extended to diisopropylnaphthalenes. Given the model's expected uncertainty intervals, COSMO-RS predictions of aqueous solubilities, (subcooled) vapor pressures, Henry's law constants, as well as octanol-water partition coefficients, are in agreement with available literature data. Simultaneous overestimation of aqueous solubilities and vapor pressures of comparable magnitude leads to partial error cancellation in the Henry's law constants. Based on physico-chemical property data obtained with COSMO-RS, the Mackay Level III fugacity model, a steady-state, non equilibrium, and regional-scale model, has been applied to exemplary evaluate the tendency of 2,6-diisopropylnaphthalene to migrate between media by modelling emissions to each individual medium and calculating the amount present at steady state.

Achieving highly accurate thermochemical predictions from relatively low levels of electronic structure theory has long been a goal of computational chemistry. One route to such a goal is to exploit the systematic cancellation of errors. This approach was spearheaded by the Pople group in the 1970s with the introduction of isodesmic bond-separation reactions, and then extended by other groups to homodesmotic (HD) and hyperhomodesmotic reactions over the ensuing years. Unfortunately, the propagation of multiple, nonequivalent definitions of HD reactions, accompanied by a panoply of related reaction classes, has lead to a great deal of confusion. We review recent efforts to introduce a refined hierarchy of HD reactions for use in thermochemical predictions and to quantify the degree of error cancellation that can be achieved. Examples of the use of reactions from the HD hierarchy from the literature are presented, as are current limitations of this HD hierarchy for thermochemistry. Although the use of such error-balanced reactions are no longer mandatory for high-accuracy thermochemical predictions of small molecules, they still offer significant advantages in this context, and offer one route to accurate thermochemical predictions of larger molecules. © 2011 John Wiley & Sons, Ltd.

In this work, we define an isodesmicity index, which allows the evaluation of the conservation of the error within a given bond conserving reaction. This index is reaction-specific and, therefore, does not rely on the nature of the reference systems. Several aspects of the index are tested, to verify that this measurement shows the desired behavior. The index is a tool, which should allow the user to establish the “best” bond conserving process for, for instance, the determination of a heat of formation.

Accurate device models are very important for the design of high-frequency circuits. One of the factors degrading the accuracy of device models appears during the de-embedding procedure. Generally, to obtain device characteristics without parasitic elements such as pads, a de-embedding procedure is essential. However, some errors are introduced during this procedure, which degrades the accuracy of device models. In this paper, we demonstrate that such errors due to de-embedding are cancelled in cascade circuit design, meaning that cascade circuits can be designed without knowing the actual characteristics of devices. Because it is difficult to know the actual characteristics of devices at a high frequency, the cancellation of the de-embedding error is expected to improve the accuracy of device models at high frequencies. After giving a theoretical treatment of de-embedding error cancellation, we report the results of simulations and measurements performed for verification.

The electronic spectra of monooxo complexes of rhenium(V) with 1,2-benzenedithiolato (bdt 2− ), 3,4-toluenenedithiolato (tdt 2− ), maleonitriledithiolato (mnt 2− ), and 1,2-dithiooxalato (dto 2− ) ligands were investigated at the TD-DFT level employing several functionals and basis sets. The most important transitions are due to ligand-to-metal charge transfer (LMCT) with some minor contribution of ligand-to-metal-ligand charge transfer (LMLCT). However, for [ReO(dto) 2 ] − this statement does not hold because the transitions are due to metal-ligand-to-metal-ligand charge transfer (MLMLCT). This observation arises from the presence of the oxalate groups. These substituents increase the flexibility of this complex with respect to the complexes containing bdt 2− , mnt 2− and tdt 2− . In these complexes, the C–C backbone imposes a rigid geometry, which leads to the occupied rhenium-orbitals lying energetically below the sulfur-based orbitals. For the complexes [ReO(bdt) 2 ] − , [ReO(mnt) 2 ] − and [ReO(tdt) 2 ] − , the HOMO is a sulfur-based out-of-plane molecular orbital. However, the HOMO of [ReO(dto) 2 ] − shows a high contribution of the rhenium d x 2 − y 2 and in-plane sulfur-centered orbitals. The comparison of the results obtained with several functionals clearly point to the PBE1PBE/LANL2DZ method as the best TD-DFT method to investigate the electronic spectra of monooxo complexes of Re(V) with thiolato ligands. The results obtained with larger basis sets suggest that the agreement between experiment and theory was due to an error cancellation between basis set incompleteness and deficiencies in the DFT methods.

In this paper, we propose computationally efficient channel estimation methods to minimize energy leakage which is caused by non-sample-spaced channels as well as band-limited OFDM signal with virtual subcarriers. The energy leakage effect mainly resulted from conventional channel estimation methods which do not utilize channel statistics information for low complexity such as DFT-based estimation and correlation error cancellation (CEC). The proposed methods solve the problem through a modified non-ideal correlation function which is derived by expanded DFT. Simple analyses and simulation results verify that the proposed methods can achieve MSE performance close to that of optimal LMMSE estimation with sufficiently low complexity.

Impulsive noise error cancellation in Orthogonal frequency division multiplexing (OFDM) system plays crucial role to determine overall performance bit error rate (BER). An algorithm of impulsive noise error cancellation, particularly for small size OFDM, was introduced by Jack K. Wolf in 1983. This algorithm determines parallelism between OFDM and Reed Solomon Code. Employing two zeros as redundancy in consecutive way in the transmitted data, the algorithm is capable to correct one additive impulsive noise error in the channel. Nevertheless, the estimation of amplitude impulsive noise is still poor. This caused by Gaussian amplification factor in the estimation amplitude of impulsive noise technique introduced by Jack K. Wolf. By removing this amplification factor the paper showing a better result in BER.

This paper describes a PSRR enhancing method for the all-digital phase-locked loop (ADPLL) by utilizing a self-regulated gated ring-oscillator (SR-GRO) time-to-digital converter (TDC) and a voltage regulator just for a digitally-controlled oscillator (DCO). The SR-GRO employs a replica supply noise monitoring circuit which tracks supply noise and enables feed-forward error cancellation over broad spectrum. A prototype ADPLL implemented in 65nm CMOS achieves >25dB PSRR when 100mV pp 1MHz supply noise is injected to both the TDC and the DCO. Experimental results show that the SR-GRO TDC can also suppress the supply coupling induced phase noise.

Kohn–Sham density-functional theory (DFT) within the local-density approximation (LDA) or the generalized-gradient approximation (GGA) is known to fail for the correct description of London dispersion interactions. Often, not even bound potential-energy surfaces are obtained for van der Waals complexes, unless special correction schemes are employed. In contrast to that, there has been some evidence for the fact that subsystem-based density functional theory produces interaction energies for weakly bound systems which are superior to Kohn–Sham DFT results without dispersion corrections. This is usually attributed to an error cancellation between the approximate exchange–correlation and non-additive kinetic-energy functionals employed in subsystem DFT. Here, we investigate the accuracy of subsystem DFT for weakly interacting systems in detail, paying special attention to the shape of the potential-energy surfaces (PESs). Our test sets include the extensive S22x5 and S66x8 data sets. Our results indicate that subsystem DFT PESs strongly vary depending on the functional. LDA results are usually quite good, but behave differently from their KS counterparts. GGA results from the popular Perdew–Wang (PW91) set of functionals produce PESs that are often, but not in general overbinding. Results from Becke–Perdew (BP86) GGAs, by contrast, show the typical problems known from the corresponding KS results. We provide some preliminary results for empirical corrections for both PW91 and BP86 in subsystem DFT.

Fusion potentials are calculated for a number of reactions within the static Hartree-Fock method with the Skyrme force SkM*. Fusion barriers agree with the data considerably better than reaction Q values. This suggests some error cancellation, possibly with the relative kinetic energy term. Our results are consistent with the idea of fusion hindrance in tip collisions. Some comparison to results of the frozen density method is made.

For seventeen molecules, complete basis set (CBS) geometries are obtained for Moller–Plesset perturbation methods at second (MP2), fourth (MP4), and sixth order (MP6) as well as for the Coupled Cluster methods CCD, CCSD, and CCSD( T ). The correlation consistent basis sets cc-pVDZ, cc-pVTZ, and cc-pVQZ were systematically applied and calculated geometries extrapolated to the limit of an infinitely large basis set. MP6 equilibrium geometries are more accurate than MP2 or MP4 geometries at the CBS limit and provide AH bond lengths with an accuracy of 0.001 A. However, AB bonds are always predicted too long because of the lack of sufficient coupling effects between p-electron correlation at MP6. CCSD( T ) provides reasonable AB bond lengths although these are in general too short by 0.003 A. Due to error cancellation very accurate geometries are obtained at the CCSD( T )/cc-pVTZ and CCSD( T )/cc-pVQZ level of theory. With the help of the accurate equilibrium geometries obtained in this work, several experimentally based geometries could be corrected. The effects of HF-optimized basis sets, diffuse functions or the frozen core approximation on geometry optimizations are discussed. It is emphasized that the use of the cc-pVDZ or any other VDZ+P basis set should be avoided in correlation corrected ab initio calculations.

We have assessed the performance of the non-self-consistent random phase approximation (RPA) on two pressure-induced structural phase transitions, diamond to \ensuremath{\beta}-Sn Si in Si and \ensuremath{\alpha}-quartz to stishovite in SiO${}_{2}$. The calculated equilibrium lattice properties of the four structures are in better agreement with experimental results than are those from several semilocal functionals. The energy differences between the high- and low-pressure phases are found to be 0.37 eV/Si and 0.39 eV/SiO${}_{2}$, respectively. The transition pressure obtained from our RPA calculations for diamond to \ensuremath{\beta}-Sn in Si is 12.2 GPa, in excellent agreement with the experimental value 11.3--12.6 GPa. However, the \ensuremath{\alpha}-quartz to stishovite phase-transition pressure in SiO${}_{2}$ is found to be 5.6 GPa, lower than the experimental 7.46 GPa; the Perdew-Burke-Ernzerhof (PBE) semilocal functional gives the transition pressure closest to experiment in this case. We conclude that the non-self-consistent, nonlocal RPA accurately describes the insulator-to-metal transition in Si, where semilocal density functionals tend to fail. But the RPA error cancellation that is nearly perfect in many solids, including Si, may be less perfect in solid SiO${}_{2}$, as it is in many molecules.

We analyze the accuracy of the frozen density embedding (FDE) method, with hybrid and orbital-dependent exchange-correlation functionals, for the calculation of the total interaction energies of weakly interacting systems. Our investigation is motivated by the fact that these approaches require, in addition to the non-additive kinetic energy approximation, also approximate non-additive exact-exchange energies. Despite this further approximation, we find that the hybrid/orbital-dependent FDE approaches can reproduce the total energies with the same accuracy (about 1 mHa) as the one of conventional semi-local functionals. In many cases, thanks to error cancellation effects, hybrid/orbital-dependent approaches yield even the smallest error. A detailed energy-decomposition investigation is presented. Finally, the Becke-exchange functional is found to reproduce accurately the non-additive exact-exchange energies also for non-equilibrium geometries. These performances are rationalized in terms of a reduced-gradient decomposition of the non-additive exchange energy.

Achieving highly accurate thermochemical predictions from relatively low levels of electronic structure theory has long been a goal of computational chemistry. One route to such a goal is to exploit the systematic cancellation of errors. This approach was spearheaded by the Pople group in the 1970s with the introduction of isodesmic bond-separation reactions, and then extended by other groups to homodesmotic (HD) and hyperhomodesmotic reactions over the ensuing years. Unfortunately, the propagation of multiple, nonequivalent definitions of HD reactions, accompanied by a panoply of related reaction classes, has lead to a great deal of confusion. We review recent efforts to introduce a refined hierarchy of HD reactions for use in thermochemical predictions and to quantify the degree of error cancellation that can be achieved. Examples of the use of reactions from the HD hierarchy from the literature are presented, as are current limitations of this HD hierarchy for thermochemistry. Although the use of such error-balanced reactions are no longer mandatory for high-accuracy thermochemical predictions of small molecules, they still offer significant advantages in this context, and offer one route to accurate thermochemical predictions of larger molecules. © 2011 John Wiley & Sons, Ltd.

Signature analyzers are very efficient output response compactors for BIST design. The only limitation of signature analysis is the fault coverage reduction (aliasing) due to the information loss inherent to any data compaction. In this article, in order to increase the effectiveness of ROM BIST, we take advantage from the simplicity of the error patterns generated by ROMs and we show that aliasing free signature analysis can be achieved in ROM BIST.

An improved analysis of a recently proposed current-mode integrator [1] is presented. The analysis includes the parasitic serial resistance on port X of the current conveyor. The feasibility of obtaining an error cancellation is considered.

The phase stability of LaMnO${}_{3}$ with respect to its competing oxides is studied using hybrid-exchange density functional theory (DFT) as implemented in crystal09. The underpinning DFT total-energy calculations are embedded in a thermodynamic framework that takes optimal advantage of error cancellation within DFT. It has been found that by using the ab initio thermodynamic techniques described here, the standard Gibbs formation energies can be calculated to a significantly greater accuracy than was previously reported (a mean error of 1.6% with a maximum individual error of $\ensuremath{-}$3.0%). This is attributed to both the methodology for isolating the chemical potentials of the reference states, as well as the use of the Becke, three-parameter, Lee-Yang-Parr (B3LYP) functional to thoroughly investigate the ground-state energetics of the competing oxides.