The basic construction of ECPs involves reproducing valence one-particle eigenvalues and closely related one-particle orbital norm conservation, i.e., the amount of valence charge outside an appropriate effective ion radius. 11 Since the number of core states and their spatial properties vary, each angular momentum symmetry channel requires a different effective potential resulting in ...A new generation of effective core potentials: selected Lanthanides and heavy elements. We construct correlation-consistent effective core potentials (ccECPs) for a selected set of heavy atoms and f-elements that are of significant current interest in materials and chemical applications, including Y, Zr, Nb, Rh, Ta, Re, Pt, Gd, and Tb.The Hellmann-Feynman force method is combined with the effective-core potential (ECP) method. Based on a theorem previously reported, we have added derivative AOsr' to the original basis r, and confirmed that the wavefunctions of the ECP method essentially satisfy the Hellmann-Feynman (HF) theorem.This makes it easier to apply an intuitive force concept quantitatively to molecular systems ...Accordingly, we present in this paper a report on the capability of various ab initio effective core potential calculations in reproducing the coordination polyhedron geometries of lanthanide complexes. Starting with all combinations of HF, B3LYP and MP2(Full) with STO-3G, 3-21G, 6-31G, 6-31G* and 6-31+G basis sets for [Eu(H2O)9]3+ and closing ...We would like to show you a description here but the site won't allow us.In order to extend neural network electronic structure cal-culations to larger systems, the computation complexity has to be reduced and one helpful approach is the so-called effective core potential (ECP) method (also known as pseudopotential). See Ref. [21] for a review. Electrons in each system can be divided into core electrons and valence ...In previous work we have shown that the PBE0 hybrid density functional method with the MG3 all-electron basis set is an accurate method for calculating the atomization energies of small aluminum clusters (Al 2-Al 7).However, the MG3 basis set is very expensive for molecules much larger than Al 13; therefore, we have developed a new effective core potential (ECP) method for aluminum to reduce ...We introduce new correlation consistent effective core potentials (ccECPs) for the elements I, Te, Bi, Ag, Au, Pd, Ir, Mo, and W with 4d, 5d, 6s, and 6p valence spaces. These ccECPs are given as a sum of spin-orbit averaged relativistic effective potential (AREP) and effective spin-orbit (SO) terms.Effective core potential integral and gradient evaluations are accelerated via implementation on graphical processing units (GPUs). Two simple formulas are proposed to estimate the upper bounds of the integrals, and these are used for screening. A sorting strategy is designed to balance the workload between GPU threads properly.tive core potentials (ECP) have been being used widely to date for many types of molecules, due to their advantages [8, 20, 21]. Using ECP basis sets, helps to reduce the computational cost significantly, over the all electron basis sets, by replacing complete group of the inner electrons with a representative effective core potential [1, 22, 23].1. Introduction. Relativistic effective core potential (RECP) methods, also called relativistic pseudopotential (PP) methods, are probably the most successful approximate methods for the various properties of molecules containing heavy atoms, since RECP calculations economically yield results that are very close to the all-electron …A consistent set of ab initio effective core potentials (ECP) has been generated for the main group elements from Na to Bi using the procedure originally developed by Kahn. The ECP's are derived from all‐electron numerical Hartree-Fock atomic wave functions and fit to analytical representations for use in molecular calculations.Very recently, we introduced a set of correlation consistent effective core potentials (ccECPs) constructed within full many-body approaches. By employing significantly more accurate correlated approaches, we were able to reach a new level of accuracy for the resulting effective core Hamiltonians. We also strived for simplicity of …Comments on "Effective Core Potentials" [M.Dolg, Modern Methods and Algorithms of Quantum Chemistry (Ed. by J.Grotendorst, John von Neumann Institute for Computing, J\"ulich, NIC Series, Vol.1 ...Effective core potentials (ECPs) are a useful means of replacing the core electrons in a calculation with an effective potential, thereby eliminating the need for the core basis functions, which usually require a large set of Gaussians to describe them. In addition to replacing the core, they may be used to represent relativistic effects, which ...Dec 23, 2023 · Calculate electronic excited states using neural networks with effective core potential. The essence of atomic structure theory, quantum chemistry, and computational materials science is solving the multi-electron stationary Schrödinger equation. The Quantum Monte Carlo-based neural network wave function method has surpassed traditional post ... Comments on "Effective Core Potentials" [M.Dolg, Modern Methods and Algorithms of Quantum Chemistry (Ed. by J.Grotendorst, John von Neumann Institute for Computing, J\"ulich, NIC Series, Vol.1 ...Effective core potential (ECP) integrals are amongst the most difficult one-electron integrals to calculate due to the projection operators. The radial part of these operators may include r⁰, r ...In previous work we have shown that the PBE0 hybrid density functional method with the MG3 all-electron basis set is an accurate method for calculating the atomization energies of small aluminum clusters (Al 2-Al 7).However, the MG3 basis set is very expensive for molecules much larger than Al 13; therefore, we have developed a new effective core …Effective core potentials (ECPs) are a useful means of replacing the core electrons in a calculation with an effective potential, thereby eliminating the need for the core basis functions, which usually require a large set of Gaussians to describe them. In addition to replacing the core, they may be used to represent relativistic effects, which ...Comments on "Effective Core Potentials" [M.Dolg, Modern Methods and Algorithms of Quantum Chemistry (Ed. by J.Grotendorst, John von Neumann Institute for Computing, J\"ulich, NIC Series, Vol.1 ...Ab initio effective core potentials (ECP's) have been generated to replace the innermost core electron for third‐row (K-Au), fourth‐row (Rb-Ag), and fifth‐row (Cs-Au) atoms. The outermost core orbitals—corresponding to the ns2np6 configuration for the three rows here—are not replaced by the ECP but are treated on an equal footing with the nd, (n+1)s and (n+1)p valence orbitals.May 7, 2021 · Besides, for these heavier elements the relativistic effects become important. One way to solve both problems simultaneously is to fit an effective core potential (ECP) to describe the core electrons using relativistic calculations, reducing the computational problem by treating only the valence electrons explicitly [22, 25, 27]. Most ECP ... Effective core potential integral and gradient evaluations are accelerated via implementation on graphical processing units (GPUs). Two simple formulas are …The Effective Core Potential Method. Ulf Wahlgren. Chapter. 884 Accesses. 3 Citations. Part of the book series: Lecture Notes in Chemistry ( (LNC,volume 58)) Abstract. The …In order to study larger systems while retaining sufficient accuracy, we integrate a powerful neural-network based model (FermiNet) with the effective core potential method, which helps to reduce the complexity of the problem by replacing inner core electrons with additional semi-local potential terms in Hamiltonian.1. Introduction. Relativistic effective core potential (RECP) methods, also called relativistic pseudopotential (PP) methods, are probably the most successful approximate methods for the various properties of molecules containing heavy atoms, since RECP calculations economically yield results that are very close to the all-electron results without introducing any empirical parameters [1, 2, 3, 4].Relativistic compact effective potentials (RCEP), which replace the atomic core electrons in molecular calculations, have been derived from numerical Dirac-Fock atomic wavefunctions using shape-consistent valence pseudo-orbitals and an optimizing procedure based on an energy-overlap functional. Potentials are presented for the third-, fourth-, and fifth-row atoms of the Periodic Table ...Effective core potentials are analyzed from the standpoint of the underlying frozen core approximation. The content of the pseudoorbital, the content of the potential, and the properties of both are elaborated, showing the points at which they differ from the frozen core approximation and where possible deficiencies might lie.Accordingly, we present in this paper a report on the capability of various ab initio effective core potential calculations in reproducing the coordination polyhedron geometries of lanthanide complexes. Starting with all combinations of HF, B3LYP and MP2(Full) with STO-3G, 3-21G, 6-31G, 6-31G* and 6-31+G basis sets for [Eu(H2O)9]3+ and closing ...Calculate electronic excited states using neural networks with effective core potential. The essence of atomic structure theory, quantum chemistry, and computational materials science is solving the multi-electron stationary Schrödinger equation. The Quantum Monte Carlo-based neural network wave function method has surpassed traditional post ...Aug 2, 2022 · We introduce new correlation consistent effective core potentials (ccECPs) for the elements I, Te, Bi, Ag, Au, Pd, Ir, Mo, and W with 4 d, 5 d, 6 s, and 6 p valence spaces. These ccECPs are given as a sum of spin-orbit averaged relativistic effective potential (AREP) and effective spin–orbit (SO) terms. Feb 11, 2021 · We propose a Monte Carlo method which exploits that core regions are physically independent in a molecule to almost remove their contribution to the numerical cost. The method is tantamount to computing an effective core potential on the fly, by efficiently subsampling the core regions with independent sidewalks. The removal of fluctuations in the core region enables also the dynamic in the ... The new method, called effective group potential, which generalizes the concept of effective core potential by including in a potential the effects of many atoms ligand, is used to calculate ...The SDD effective core potential basis set is not suitable for the bond length calculation for PBDEs. The results of the two methods are close to the experimental data, while the all-electron basis set is more suitable for the bond length calculation for PBDEs than the SDD effective core potential basis set. The results show that the calculated ...A generalization of the shape‐consistent Relativistic Effective Core Potential (RECP) method is developed for the case of pseudospinors that may have nodes. Both valence and outermost core pseudospinors are included in the Generalized RECP generation procedure.An effective core potential system has been developed for heavy atoms in which relativistic effects are included in the effective potentials (EP). The EP's are based on numerical Dirac-Hartree-Fock calculations for atoms and on the Phillips-Kleinman transformation with other aspects similar to the treatments of Goddard and Melius and ...The pseudopotential is an effective potential constructed to replace the atomic all-electron potential (full-potential) such that core states are eliminated and the valence electrons …Fermionic neural network with effective cor e potential. Xiang Li ,1,*Cunwei Fan ,2,†Weiluo Ren,1and Ji Chen 3, 1 ByteDance Inc., Zhonghang Plaza, No. 43, North 3rd Ring West Road, Haidian ...The new method, called effective group potential, which generalizes the concept of effective core potential by including in a potential the effects of many atoms ligand, is used to calculate ...calculation of effective core potential (ECP) integrals in quantum chemistry codes - GitHub - chrr/libECP: calculation of effective core potential (ECP) integrals in quantum chemistry codesGeneralized Relativistic Effective Core Potential Method: Theory and calculations. A.V.Titov, N.S.Mosyagin. In calculations of heavy-atom molecules with the shape-consistent Relativistic Effective Core Potential (RECP), only valence and some outer-core shells are treated explicitly, the shapes of spinors are smoothed in the atomic core regions ...Moreover, the DMC method can be further integrated with other powerful molecular neural networks 22,25, periodic neural network for solids 48, neural networks with effective core potential 49 ...The effective core potential (ECP) was applied to the 60electron cores of Hg and Pb and the 28-electron core of Cd to take the relativistic contraction of the cores into account [35, 36]. The M06 ...9 Effective Core Potentials. 9.1 Introduction; 9.2 ECP Fitting; 9.3 Built-In ECPs. 9.3.0.1 Combining ECPs; 9.3.0.2 Examples; 9.4 User-Defined ECPs; 9.5 ECPs and Electron Correlation; 9.6 Forces and Vibrational Frequencies with ECPs; 9.7 A Brief Guide to Q-Chem ’s Built-In ECPs; 10 Exploring Potential Energy Surfaces: Critical Points and ...The new method, called effective group potential, which generalizes the concept of effective core potential by including in a potential the effects of many atoms ligand, is used to calculate ...A generalization of the shape‐consistent Relativistic Effective Core Potential (RECP) method is developed for the case of pseudospinors that may have nodes. Both valence and outermost core pseudospinors are included in the Generalized RECP generation procedure.This work integrates a powerful neural-network based model (FermiNet) with the effective core potential method, which helps to reduce the complexity of the problem by replacing inner core electrons with additional semi-local potential terms in Hamiltonian. Deep learning techniques have opened a new venue for electronic structure theory in recent years. In contrast to traditional methods, deep ...# # Author: Qiming Sun <[email protected]> # ''' Effective core potential (ECP) This module exposes some ecp integration functions from the C implementation. Reference for ecp integral computation * Analytical integration J. Chem. Phys. 65, 3826 J. Chem. Phys. 111, 8778 J. Comput. Phys. 44, 289 * Numerical integration J. Comput.The relevant key words are, for example, B3LYP/Gen pseudo=cards. Also, the effective core potential and the related basis set need to be placed explicitly after the coordinates of atoms in the ...Abstract: The ab initio model potential method and its applications to atoms, molecules, and solids are reviewed here stressing its main characteristic of enabling a common computational strategy for effective core potential calculations in molecules and embedded cluster calculations of defects in solids and surface chemistry. As an effective …New correlation consistent basis sets for the second-row atoms (Al-Ar) to be used with the neon-core correlation consistent effective core potentials (ccECPs) have been developed. The basis sets, denoted cc-pV(n+d)Z-ccECP (n = D, T, Q), include the "tight"-d functions that are known to be important for second-row elements. Sets augmented with additional diffuse functions are also ...May 7, 2021 · Besides, for these heavier elements the relativistic effects become important. One way to solve both problems simultaneously is to fit an effective core potential (ECP) to describe the core electrons using relativistic calculations, reducing the computational problem by treating only the valence electrons explicitly [22, 25, 27]. Most ECP ... Diagram of a fluorine atom showing the extent of effective nuclear charge. (CC BY-SA 3.0; NikNaks via Wikipedia). The charge \(Z\) of the nucleus of a fluorine atom is 9, but the valence electrons are screened appreciably by the core electrons (four electrons from the 1s and 2s orbitals) and partially by the 7 electrons in the 2p orbitals.Effective core potential integral and gradient evaluations are accelerated via implementation on graphical processing units (GPUs). Two simple formulas are proposed to estimate the upper bounds of the integrals, and these are used for screening. A sorting strategy is designed to balance the workload …[Show full abstract] (FermiNet) with the effective core potential method, which helps to reduce the complexity of the problem by replacing inner core electrons with additional semilocal potential ...Efficient implementation of effective core potential integrals and gradients on graphical processing unitsEffective core potentials (ECPs) are crucial in applying quantum chemical methods to heavier elements. The associated ECP integrals are among the most difficult one-electron integrals to calculate. In Q-Chem 5.0, a new state-of-the-art ECP integral engine was introduced, exploiting efficient screening and recurrence relations.有効内核ポテンシャル（英: effective core potential, ECP）とも呼ばれる。 こうした擬ポテンシャルは、内核電子が与える静電相互作用や交換相関相互作用とは全く無関係に、原子核から或る半径よりも外側では、波動関数が全電子計算の結果と一致することだけ ...The FCH potential (the self-consistent field resulting from the core-hole orbital constraint) defines a full spectrum of effective single-particle orbitals, which can be computed explicitly up to high energies in order to determine the transition probabilities, or the associated core-excited spectral function (related to the imaginary part of ...The relevant key words are, for example, B3LYP/Gen pseudo=cards. Also, the effective core potential and the related basis set need to be placed explicitly after the coordinates of atoms in the ...Effective Core Potential - By Dolg - Free download as PDF File (.pdf), Text File (.txt) or read online for free. Michael dolg outlines the basic ideas of the relativistic ab initio effective core potential method. The underlying approximations as well as the differences between the two commonly used versions, i.e., model potentials and pseudopotentials, are discussed.A new 11-electron relativistic effective core potential (11e-RECP) for Ag atom based on correlated level of theory and the associated atomic orbital (AO) basis set have been derived which allows for an accurate determination of excited states. This has been verified by comparing the calculated excited states of the dimer with experimental …Oct 5, 2012 · We present a set of effective core potential (ECP) basis sets for rhodium atoms which are of reasonable size for use in electronic structure calculations. In these ECP basis sets, the Los Alamos ECP is used to simulate the effect of the core electrons while an optimized set of Gaussian functions, which includes polarization and diffuse ... Generalized Relativistic Effective Core Potential Method: Theory and calculations. A.V.Titov, N.S.Mosyagin. In calculations of heavy-atom molecules with the shape-consistent Relativistic Effective Core Potential (RECP), only valence and some outer-core shells are treated explicitly, the shapes of spinors are smoothed in the atomic core regions ...We would like to show you a description here but the site won’t allow us.EFFECTIVE CORE POTENTIALS MICHAEL DOLG Institut f ur Physikalische und Theoretische Chemie, Wegelerstr. 12, 53115 Bonn Germany E-mail: [email protected] After a brief review of relativistic e ects on the electronic structure of atoms and molecules the basic ideas of the relativistic ab initio e ective core potential method are outlined.Effective Core Potential Methods. Derivation of Effective Core Potentials and Valence Basis Sets. Computational Methods. Representative Examples: Main Group Chemistry. Representative Examples: Transition Metal and Lanthanide Chemistry. Summary and ProspectusFeb 22, 1999 · A new 11-electron relativistic effective core potential (11e-RECP) for Ag atom based on correlated level of theory and the associated atomic orbital (AO) basis set have been derived which allows for an accurate determination of excited states. This has been verified by comparing the calculated excited states of the dimer with experimental data. Gropen et al./Effective core potential calculations on JVZW~ Table 2 Computed barriers a) Value within parentheses is the computed barrier obtained with the basis set used for the Huzinaga-type model poten- tials. Frozen core calculations (method 2) give virtually exactly the same results as the full calculations, indi- cating that core ...A method is described for obtaining l‐dependent relativistic effective core potentials (ECPs) from Dirac–Fock self‐consistent field atomic wave functions. These potentials are designed for use in nonrelativistic (NR) valence electron Hartree–Fock calculations on atoms and molecules. The novel aspect of this approach involves the averaging of the separately …However, in your ECP calculation, the core electrons of lithium are not described explicitly. So the energy zero point is the state where a $\ce{Li+}$ cation, a $\ce{H+}$, and two electrons are infinitely far away from each other. This is of course a considerably lower reference energy than the all-electron case, because the two core electrons ...We introduce new correlation consistent effective core potentials (ccECPs) for the elements I, Te, Bi, Ag, Au, Pd, Ir, Mo, and W with 4d, 5d, 6s, and 6p valence spaces. These ccECPs are given as a sum of spin-orbit averaged relativistic effective potential (AREP) and effective spin–orbit (SO) terms.The idea of effective core potentials (ECPs) is based on the chemically intuitive restriction of the explicit calculations to the chemical important valence electrons, while the essentially inert atomic cores, i.e., the nucleus and the electrons in the inner shells, are replaced by a suitable parametrized (relatively simple) one-electron operator acting on the remaining valence electrons, i.e ...Effective core potential integral and gradient evaluations are accelerated via implementation on graphical processing units (GPUs). Two simple formulas are proposed to estimate the upper bounds of the integrals, and these are used for screening. A sorting strategy is designed to balance the workload between GPU threads properly.Fermionic neural network with effective cor e potential. Xiang Li ,1,*Cunwei Fan ,2,†Weiluo Ren,1and Ji Chen 3, 1 ByteDance Inc., Zhonghang Plaza, No. 43, North 3rd Ring West Road, Haidian ...Even today, in spite of the development of fast computers and new efficient methods, the complexity of molecular calculations is rapidly increasing with the number of electrons. Quantum mechanical calculations on molecules containing first- and second-row atoms are now a routine task. The third-row atoms are certainly more complicated, owing to ...An effective core potential is a basis function (a pseudo -orbital) that is used to “substitute” the inner (core) electrons of an atom. The pseudo-orbitals are formulated to be nodeless in the core region ( Figure 1 ). 4 It provides a relativistic effective potential for each core orbital eliminating the need for core basis functions and ...Effective core potential (ECP) integrals are amongst the most difficult one-electron integrals to calculate due to the projection operators. The radial part of these operators may include r⁰, r ...The computational investigations of lanthanide complexes using relativistic effective core potential (ECP) [60][61][62] in conjugation with density functional theory (DFT) provide accurate results ...tive core potentials (ECP) have been being used widely to date for many types of molecules, due to their advantages [8, 20, 21]. Using ECP basis sets, helps to reduce the computational cost significantly, over the all electron basis sets, by replacing complete group of the inner electrons with a representative effective core potential [1, 22, 23].We construct correlation-consistent effective core potentials (ccECPs) for a selected set of heavy atoms and f elements that are currently of significant interest in materials and chemical applications, including Y, Zr, Nb, Rh, Ta, Re, Pt, Gd, and Tb. As is customary, ccECPs consist of spin-orbit (SO) averaged relativistic effective potential (AREP) and effective SO terms.An improved effective core potential (ECP) technique is described and used to give ECP parameters for the atoms of the first two rows of the periodic table. A …Semantic Scholar extracted view of "The ab initio Model Potential Method: A Common Strategy for Effective Core Potential and Embedded Cluster Calculations" by L. Seijo et al. Skip to search form Skip to main content Skip to account menu. Semantic Scholar's Logo. Search 216,897,579 papers from all fields of science ...In our previous work we examined DFT using all-electron basis sets, but approaches incorporating effective core potentials (ECPs) are effective in reducing computational expense. With this in mind, our efforts were expanded to include evaluation of the performance of the basis set derived to approximate such an approach as well on the same set ...Good agreement between the calculated and experimental geometries was obtained. Although the size of the effective core potential (ECF) basis sets is about half or less than those of the non-ECP basis sets, 6-31G(p) and 6-311G(d,p), the obtained average errors and scale factors were comparable to those obtained using the non-ECP basis sets.A method is described for obtaining l‐dependent relativistic effective core potentials (ECPs) from Dirac–Fock self‐consistent field atomic wave functions. These potentials are designed for use in nonrelativistic (NR) valence electron Hartree–Fock calculations on atoms and molecules. The novel aspect of this approach involves the averaging of the separately …The ground state geometries of small neutral Ag n (n=2–9) and cationic Ag n + (n=2–9) clusters have been determined in the framework of the Hartree–Fock and complete active space self‐consistent field (CASSCF) procedure employing a relativistic effective core potential (RECP) accounting for core–valence correlation effects (CVC). …This is commonly accomplished by introducing effective core potentials (ECPs) or closely related pseudopotentials, that open opportunities to study systems with hundreds of valence electrons. ... the nonlocal integrals can be carried out explicitly saving thus the computational time while generating a different effective potential and ...
The generalized relativistic effective core potential (GRECP) method is analyzed from theoretical and computational points of view. The Hamiltonian in the frozen-core approximation is compared with the Hamiltonian containing the GRECP operator. It is demonstrated that the GRECP operator can be derived from rather natural physical grounds and .... Atacama desert latin america
Effective core potentials derived from these revised pseudo‐orbitals were used to compute potential energy curves for the ground states of F2, Cl2, and LiCl and the results are compared with previous all‐electron and effective potential calculations.Effective core potential (ECP) integrals are amongst the most difficult one-electron integrals to calculate due to the projection operators. The radial part of these operators may include r⁰, r ...Effective core potentials (ECPs) are widely used in electronic structure calculations of molecular and condensed systems. ... Clearly, more elaborate parameterizations are possible for finer accuracy targets. For instance, core-polarization effects and explicit spin-orbit coupling operators could be added subsequently, but that is …A new contraction of the basis sets associated with the Hay-Wadt relativistic effective core potentials (RECPs) for the main group and transition metal atoms are suggested, more suitable for density functional theory investigations than the previous 'double-ζ' contractions based upon Hartree-Fock atomic results. We suggest a new contraction of the basis sets associated with the Hay-Wadt ...Abstract: The ab initio model potential method and its applications to atoms, molecules, and solids are reviewed here stressing its main characteristic of enabling a common computational strategy for effective core potential calculations in molecules and embedded cluster calculations of defects in solids and surface chemistry. As an effective core …We have used effective core potential (def2-ECP) 43, 46 to treat the chemically inert gold core electrons in all our optimization and SPE calculations. Furthermore, to investigate the relativistic ... You signed in with another tab or window. Reload to refresh your session. You signed out in another tab or window. Reload to refresh your session. You switched accounts on another tab or window. Effective core potential integral and gradient evaluations are accelerated via implementation on graphical processing units (GPUs). Two simple formulas are proposed to estimate the upper bounds of the integrals, and these are used for screening. A sorting strategy is designed to balance the workload …The pseudopotential is an effective potential constructed to replace the atomic all-electron potential (full-potential) such that core states are eliminated and the valence electrons …Effective Core Potential methods are classified in two families, according to their basic grounds. On the one hand, the Pseudopotential methods (PP) rely on an orbital transformation called the pseudoorbital transformation and they are ultimately related to the Phillips-Kleinman equation [2]. On the other hand, the Model Potential methods (MP ...This is commonly accomplished by introducing effective core potentials (ECPs) or closely related pseudopotentials, that open opportunities to study systems with hundreds of valence electrons. ... the nonlocal integrals can be carried out explicitly saving thus the computational time while generating a different effective potential and ...Effective core potentials. Pseudopotentials (effective core potentials, ECPs) may be defined at the beginning of BASIS blocks. The general form of the input cards is. which defines a pseudopotential for an atom specified either by a chemical symbol or a group number. The ECP specification may consist either of a single keyword, which references ....