bluuebunny/crossref_metadata_2025_split huggingface dataset:
Assigning Tasks and Leadership Responsibilities
Authors: Susskind Lawrence E , Cruikshank Jeffrey L 
Published: November 2023

Abstract
In previous chapters, we’ve described the group dynamics dictated by Robert’s Rules—a parliamentary approach that, at the end of the day, is all about process. But another way to compare Robert’s Rules with CBA is to look at the players involved. What roles do they play? What are their respective responsibilities? Perhaps most important, where does leadership come from, and how is it exercised? In parliamentary procedure, there are really only four players. These are: the public at large, the deliberative body (which we’ll consider collectively as one player), the moderator (or chair), and in some cases, the parliamentarian. Let’s look briefly at their roles and responsibilities. The general public is at least one step removed from the action. It is almost entirely reactive, responding or failing to respond to the actions of a deliberative body like a town meeting. If the public gets angry enough about one or more issues, they can change the composition of the deliberative body, for example, at the ballot box. The deliberative body proposes and disposes, following the tight script laid down by Robert’s Rules.
Convening
Authors: Susskind Lawrence E , Cruikshank Jeffrey L 
Published: November 2023

Abstract
Anyone can initiate a consensus-building process by raising the idea with the right individual(s) or official(s) in charge. The critical step at the outset is to identify a potential convener—an elected or appointed official or a senior official in the private sector with the formal authority to take action. This person does not need to know very much about CBA in order to play a convening role. At the outset, it is crucial to discuss the advantages and disadvantages of using consensus building, rather than relying exclusively on whatever the usual way of making group decisions might be.
Über die Umkehrung der Naturgesetze
Authors: Schrödinger E 
Published: November 2023

Abstract
A decade before his 1926 paperb reporting his discovery of wave mechanics, a derivation of the time-independent wave equation, and its solutions for hydrogen-like atoms, Erwin Schrödinger had carried out several studies dealing with Brownian motion. It is clear from several of the papers he wrote that he was completely familiar with diffusion equations, the Fokker-Planck equation in many forms, their connections with Green’s functions, and with behavior of systems of particles undergoing random walks including those in force fields.c Thus, it is not surprising that Schrödinger was aware of the relation of the Schrödinger equation in imaginary time, to the diffusion equation governing particles undergoing diffusion, In this paper, with the title “On the Reversal of Natural Laws,” Schrödinger pointed out the remarkable formal analogy of diffusion with quantum mechanics and the discrepancies introduced by the factor J=T. In his discussion Schrödinger made the statement, “I am unable to foresee whether this analogy will prove itself useful in the clarification of quantum mechanical concepts,” but he finished the paper with the hope it would. There is no indication that Schrödinger was aware of the possibilities of a next step into quantum Monte Carlo - the use of random walks to provide solutions to the wave equation. This was left for others to discover later.
Spin-orbit coupling in variational quantum Monte Carlo calculations
Authors: Flad H J , Dolg M , Shukla A 
Published: November 2023

Abstract
Although several types of spin interactions had been included in earlier QMC studies in nuclear physics, this is the first paper to report QMC calculations including the spin-orbit effect for atomic systems. The problem treated is that of predicting the effect of valence electron correlation on the energies of eigenstates involving the 6s2 6p2 valence electrons of the isoelectronic species Pb, m+, and Po2+. Experimental measurements of the fine-structure splittings provided a challenging target for the authors. It was necessary to simplify the problem with a series of approximations, beginning with a pseudopotential to eliminate the 78 electrons of the Pt core. A semi-local spin-orbit-averaged relativistic pseudopotential was used for this purpose. With total spin and spatial angular momentum variable, the trial wavefunctions were expressed as linear combinations of LS-coupled wavefunctions, similar in form to functions without spin-orbit coupling, but very much more complicated in detail. The calculations were carried out in variational QMC with a generalized Metropolis algorithm, in effect diffusion with drift, but without multiplication. The results were expressed as excitation energies for the 6s2 6p2 3 A, 3 P2,1 D2, and 1 So electronic states of Pb, Bi+, and Po2+ with respect to the 3 Po ground state. The values were typically accurate within a few percent and comparable to those of equivalent all-electron and pseudopotential calculations by multireference configuration interaction methods.
Quantum Monte Carlo with model potentials for molecules
Authors: Yoshida T , Miyako G 
Published: November 2023

Abstract
Although simple model potentials lack the solid theoretical basis that justifies nonlocal pseudopotentials, they have been used with moderate success in replacing the core electrons in analytic variational calculations and in diffusion QMC calculations. For this paper, a model potential of long standing, proposed by Bonifacic and Huzinagaa in 1974, was investigated in calculations of dissociation energies for the molecules CO, HCl, Na2, and K2, The model potential has an especially simple form for the effective field of the core electrons based on core orbitals. The valence electrons are treated explicitly with Hartree-Fock orbitals used in determinantal trial functions for importance sampling and node location. The numbers of valence electrons treated were: CO, 10; HCl, 8; Na2, 2; K2, 2. In each case, the calculated dissociation energy was found to be accurate to within a few percent of the experimental value and much more accurate than either all-electron or model-potential Hartree-Fock calculations. Despite concerns about its justification, the method appears to be surprisingly successful.
Optimization of quantum Monte Carlo wave functions using analytical energy derivatives
Authors: Lin X , Zhang H , Rappe A M 
Published: November 2023

Abstract
The optimization of parameters in trial wavefunctions by minimizing the variance in local energy was used for some of the earliest variationala and diffusionb QMC calculations, and it has been used ever since by most practitioners of QMC. Perhaps the best known examples are given in the paper by Schmidt and Moskowitzc for optimizing their nine-parameter Jastrow functions for first-row atoms. An alternative method of optimization, leading to lower variational energies for these atoms, is reported in this paper.
Monte Carlo calculation of the Born-Oppenheimer potential between two helium atoms using Hylleraas-type electronic wave functions
Authors: Coldwell R L , Lowther R E 
Published: November 2023

Abstract
Solution of the Schrödinger equation using the Rayleigh-Ritz variational method in combination with numerical integration was introduced as early as 1942 by Frost.a Conroyb added the Monte Carlo aspect with random selection of points in the configuration space of electrons for molecular systems. This paper and a related paperc by the same authors reported calculations similar to those of Conroy using variational QMC to determine the electronic structure of the helium dimer. Along with this Coldwell and Lowther introduced the idea of correlated sampling for such Monte Carlo variational calculations. They used a “biased selection” procedure to select 6400 points from an approximate ψ2 distribution for evaluation of local energies and calculation of the expectation value of the energy for four internuclear distances. The trial functions were anti-symmetrized products of two Hylleraas atomic-helium functions in combination with an exponential term containing dipole-dipole and dipole-quadrupole interaction terms. The energies obtained with reasonably good trial functions gave expectation values of the energy well below the Hartree-Fock limit and in agreement within their fairly large uncertainties with experimentally based estimates of the interaction energies for two helium atoms.
Diffusion Monte Carlo study of circular quantum dots
Authors: Pederiva F , Umrigar C J , Lipparini E 
Published: November 2023

Abstract
Several QMC calculations had earlier treated quantum dots of various shapes and sizes by either variational or diffusion methods. This study extended much farther, with ground and low-lying excited states for circular two-dimensional dots with 2 to 13 electrons. The method was fixed-node diffusion QMC with importance sampling. Comparisons were made with Hartree-Fock and density functional calculations at the LSDA level. The system treated was a standard circular quantum dot with N electrons confined in two dimensions by a parabolic potential V = ½kr2 centered at the origin. The masses, dielectric constants, and the potential energy constants were specified as those for a GaAs crystal. Atomic units were replaced by effective atomic units. Anti-symmetry rules were the same as for atomic systems. Trial functions were expressed for each case as sums of one to five Slater determinants from density functional calculations, along with elaborate generalized Jastrow functions. The coefficients required for satisfying cusp conditions were different from those usually found for three-dimensional problems. A total of 23 cases with different numbers of electrons and L, S eigenstates were treated. The first version of the paper contained a few errors. Corrected results (also with lower uncertainties) were reported in a second version.0 In all cases the diffusion QMC energies were lower than the variational QMC energies, which were in turn lower than the HF energies. Fixed-node error was expected to be small. The differences from LSDA density functional energies were small but not negligible.
Elucidating the role of many-body forces in liquid water. I. Simulations of water clusters on the VRT(ASP-W) potential surfaces
Authors: Goldman N , Saykally R J 
Published: November 2023

Abstract
In the quest for a quantitative simulation of liquid water it appears the potential energy of the interaction of water molecules converges very rapidly and may be described adequately by only two- and three-body terms. Measurements of vibration-rotation tunneling (VRT) splittings for water dimers have provided data for fitting an anisotropic site potential with Woermer dispersion (ASPW) to provide a series of highly detailed potential energy surfaces. The expressions for these surfaces include terms corresponding to electrostatic interaction, two-body exchange repulsion, two-body dispersion, and many-body induction. In this paper the authors report an investigation of the suitability of these surfaces and several others for predicting the vibrational ground-state properties of water clusters ranging from the trimer to the hexamer. The calculations were carried out with diffusion Q:tvIC to determine cluster properties, the structures and, in particular, the vibrational average rotational constants for direct comparison with experimentally measured values. The ground-state properties were determined in runs for 1000 walkers with 15,000-20,000 time steps after equilibration. Histograms of configurations were used for calculating the internal tensors leading to the rotational constants.
A ground state potential energy surface for H2 using Monte Carlo methods
Authors: Alexander S A , Coldwell R L 
Published: November 2023

Abstract
Although more accurate values of ground-state electronic energies of the clamped-nucleus H2 molecule have been obtained in analytic variational calculations with explicitly correlated wavefunctions, the Monte Carlo variational calculations reported in this paper provide a useful alternative to analytic calculations. Aside from confirming energies, they may be used in straightforward and simple independent calculations of the quantities needed for nonadiabatic diagonal corrections, relativistic corrections, and radiative corrections to the Born-Oppenheimer potential energy curve. The trial functions used were symmetric exponential functions of products of electron-electron and electron-nucleus distances with integer exponents and up to 128 adjustable parameters optimized to minimize a combination of the energy and its variance. The calculations were carried out for 24 internuclear distances in the range of 0.2 to 10.0 bohr, and they gave energies typically 1-3 microhartrees above analytic variational values with uncertainties typically less than 1 microhartree. Most interesting are the correction terms, which are not variational and were found to confirm earlier values within 1 microhartree. Binding energies calculated for several vibration-rotation levels of H2 using the calculated potential energy curve were found in excellent agreement with those determined from spectroscopic measurements. The authors proposed that the Monte Carlo techniques used be generalized to larger systems for which analytic integrations are much more difficult.
Scheme for adding electron-nucleus cusps to Gaussian orbitals
Authors: Ma A , Towler M D , Drummond N D , Needs R J 
Published: November 2023

Abstract
The trial wavefunction for importance sampling in a diffusion QMC calculation for an atom or molecule has most often been assembled from a Slater determinant or a sum of determinants multiplied by a Jastrow function. The determinantal part is readily obtained from easy-to-use quantum chemistry programs which make use of Gaussian basis sets. The programs take advantage of the analytic integrals available for Gaussian exponentials, but these functions fail to give a good fit to realistic one-electron orbitals and produce large fluctuations in the local energy near the electron-nucleus cusps. One solution to the problem has been to fit the Gaussian functions to simple exponentials, adjust them to satisfy the cusp condition, and use them in the determinantsa. In this paper a new scheme, having the advantages of an automatic procedure and avoiding some of the earlier problems is reported. In this scheme a part of each s-type Gaussian function &lt;/J(r) is replaced by a new function ¢ (r) which depends on exp[p(r)] in which p(r) = Do+ a1r + D2r2 + D3r3 + D4r4. Theconstants Di and others are adjusted to fit first and second derivatives to &lt;/J(r), to satisfy the cusp condition, and to optimize the behavior of the local energy. This is accomplished analytically. The scheme was investigated in detail with VQMC and fixednode DQMC for the atom Ne and the molecule H2. Calculations were also made for the 55 molecules of a standard test set. Improvement in the standard deviation in local energy, relative to that for no cusp correction, was dramatic. In the VQMC calculations for the test set the standard deviation in individual local energy was reduced by a factor of 2 to 5 for most molecules. This corresponds to a reduction by a factor of 4 to 25 in calculation effort for a fixed statistical error. Total energies were found to be slightly reduced.
Quantum chemistry by random walk: Linear HS
Authors: Mentch F , Anderson J B 
Published: November 2023

Abstract
This is first of three papers published in 1984 which report calculations for the system H-H-H in a symmetric linear configuration matching the expected saddle point for one of the most basic chemical reactions, the exchange reaction H + H2 -+ H2 + H. In this case, the calculations were fixed-node diffusion calculations, with importance sampling made with four different types of trial functions specifying the nodal structure. Each included simple electronelectron correlation terms. The functions were optimized by minimizing the variance in the local energy H’¢T / ‘¢T using a simplex routine. The lowest energy result obtained for the minimum in the barrier to reaction was -1.6582 ± 0.0003 hartrees, corresponding to a barrier height of 10.2 ± 0.2 kcal/mol relative to the exact minimum for separated H + H2, This value was slightly below the upper bound of 10.28 kcal/mol established in analytic variational calculations and about 0.6 kcal/mol above the expected value. The difference was attributed to node location error.
Quantum Monte Carlo study of the classical barrier height for the H + H2 exchange reaction: Restricted versus unrestricted trial functions
Authors: Reynolds P J 
Published: November 2023

Abstract
In this fixed-node calculation with importance sampling for the H-H-H system, the authors investigated the use of several single determinant SCF trial functions and the effects of restricting the orbital coefficients. The true wavefunction must have identical coefficients for a and (3 electrons, but in variational calculations, the use of unrestricted spin-orbitals (allowing different coefficients) leads to energies lower than (or at least as low as) those for restricted spin-orbitals (requiring identical coefficients). This has been observed in variational QMC calculations for H-H-H. However, in fixed-node diffusion calculations, in which the energies depend only on node locations, the authors found a lower energy for restricted trial functions. For the barrier they obtained an energy of -1.6590 ± 0.0004 hartrees, a value lower than the lowest CI energy at the time, and only 9.69 ± 0.25 kcal/mol above that for separated reactants. This value is an upper bound to the barrier height, but within its uncertainty it overlaps the best recent valuea of 9.608 ± 0.001 kcal/mol.
Quantum chemistry by random walk: A faster algorithm
Authors: Anderson J B 
Published: November 2023

Abstract
This little paper describes two procedures for achieving higher speeds in fixed-node diffusion QMC calculations with importance sampling. The first is an iterative procedure for reducing timestep error, thereby allowing larger and fewer time steps to obtain a given accuracy. The movement of a walker is divided into two parts: a diffusion step selected at random from an appropriate distribution and a drift step calculated from the drift velocity at the initial location. These give a temporary step to a new location for which the drift velocity is again determined. The average of the two velocities together with the original diffusion step is used to determine a permanent step. In tests, the procedure was found to reduce time-step error by a factor of 5 to 10. The second procedure makes use of two trial functions for importance sampling, the first a simple function for walker motion and the second a more complex and more accurate function for determining energies. These allow the more computationally expensive function to be used at large intervals for samples having a lower serial correlation.
Quantum simulation of systems with nodal surfaces
Authors: Coker D F , Watts R 0. 
Published: November 2023

Abstract
Coker and Watts reported modifications of the simple diffusion QMC algorithm to treat the problem of node location in small systems. This enabled the calculation of low-lying states for a vibrating diatomic molecule as well as electronic structures for H 2p, He 3S, and Li 1S. The general method makes use of cancellation of positive and negative walkers occupying the same volume elements of a grid in the coordinate space of the walkers, together with appropriate constraints to prevent decay to a lower-energy solution. In the case of molecular vibration, orthogonality to lower states was enforced by maintaining equal weights of positive and negative walkers in equivalent regions of coordinate space for lower states. For the case of fermion ground states for He 3 S and Li 1 S, equal weights of positive and negative walkers were required for all coordinate space. For the higher dimensionality of the Li case, cancellation was based on proximity of walkers of opposite signs. Results in terms of energy were accurate to about three digits and within their uncertainties overlapped accepted values for each of the systems investigated. These provided a hint of more accurate results to be obtained later for small systems.
Quantum chemistry by quantum Monte Carlo: Beyond ground-state energy calculations
Authors: Reynolds P J , Barnett R N , Hammond B L , Grimes R M , Lester W A 
Published: November 2023

Abstract
The paper describes several extensions of fixed-node diffusion in the areas of obtaining analytic derivatives of the energies of molecules, calculating expectation values for quantities other than the energy, and treating excited states. The calculation of energy derivatives is illustrated with a calculation of the first derivative of the energy of the ground state of H2 with respect to the internuclear distance, without using finite differences. With importance sampling the energy is obtained from a weighted average of local energies expressed in analytic form. These may be differentiated to obtain their derivatives with respect to any of several variables, including the internuclear distance, and their weighted averages may be used to determine the desired derivatives. The results for the H2 energy derivatives were in agreement with independent determinations. For calculation of expectation values of the energy, sampling of the (true wavefunction)(trial wavefunction) ‘1/J’l/Jr distribution is sufficient, but other quantities usually require sampling the ‘ljJ2 distribution, which is not so readily available in QMC calculations. Extrapolations of ‘!/Jf and ‘ljJ’l/Jr results, from variational and diffusion calculations, to ‘!jJ2 results are illustrated for various expectation values for the case of ground-state H2.
Quantum chemistry by random walk: Methane
Authors: Garmer D R , Anderson J B 
Published: November 2023

Abstract
The methane molecule has served as a test case for a lengthy series of electronic structure calculations beginning in 1941 with approximate Hartree-Fock calculations and an energy of -39.47 hartrees, reaching in 1973 to 81% of the correlation energy with extended-basis CI calculations at -40.4584 h, and going much further with this paper in 1987 to 97% of the correlation energy with fixed-node diffusion QMC calculations at -40.506 h. The calculations were carried out by the fixed-node diffusion method with drift, making use of importance sampling with a single determinant trial function based on double-zeta Slater-type orbitals, along with a simple Jastrow function. This function was optimized to minimize both the energy and the variance of the local energy. Time-step error was investigated in detail with six different time-step sizes down to 0.0005 h-1, giving nearly straight line behavior. The calculated energy at -40.506(2) hartrees and 97% of the correlation energy was 31 kcal/mol lower than the lowest analytic variational energy at the time and only 5 kcal/mol above the experimental nonrelativistic energy.