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## Scholarly Works (32 results)

In today’s world of intense ideological conflict at the elite level, the nature of mass belief systems has changed dramatically since the last time Converse’s famous levels of conceptualization (Campbell et al., 1960; Converse, 1964) were coded in 2000. This paper shows that the percentage with well-developed belief systems based on a clear understanding of public policy choices has increased substantially since then. It also introduces a new category termed “policy wonks” to reflect a sub-category that Converse only referred to in passing but which is now quite common. Unlike respondents whom I classify as “concept ideologues” in this paper, policy wonks do not employ overarching concepts such as liberalism/conservatism or the scope of government. Rather, policy wonks just refer to at least three public policy stands when asked what they like and dislike about the major parties and presidential candidates. Although it was very rare for citizens in the 1950s to show a clear belief system based on the specific choices of government action, today’s highly intense and polarized policy debates have made programmatic-oriented belief systems quite common. A close examination of policy wonks shows that they are just as politically knowledgeable and consistent on issue dimensions as concept ideologues (i.e., those who employ ideological terms). Hence, policy wonks possess a well-defined belief system based on employing an understanding of public policy, thereby befitting Converse’s criteria for classification at the top level of conceptualization.

The substantial increases in both concept ideologues and policy wonks accounts for virtually all of the increase since the 1980s in respondents whose partisanship matches their ideology (i.e., conservative Republicans and liberal Democrats). Not only are respondents at the top of levels of conceptualization more numerous than they used to be, but being more consistent than they used to be has led to a marked increase in the overall correspondence between partisanship and ideology. On the other hand, the decrease in ideologically inconsistent partisans (i.e., liberal Republicans and conservative Democrats) has occurred across all conceptualization levels. Thus, party polarization is a combination of: 1) better-developed belief systems increasing ideological-partisan consistency; and 2) partisan sorting decreasing partisans who are out step with their party’s ideological stance.

Past research has shown that Republicans are substantially more likely to be ideologues whereas Democrats are much more inclined to conceptualize politics in terms of group benefits. This pattern was quite evident in the 2008 and 2012 American National Election Study (ANES) responses that I personally coded. However, two developments occurred in 2016 that dramatically reshaped the partisan nature of belief systems. First, the Bernie Sanders wing of the Democratic Party evidenced a great deal of ideological thinking, thereby pushing Democrats to a record percentage at the top level of ideological conceptualization. Second, the voters who supported Trump in the Republican primaries were much less likely to be ideologues or policy wonks than those who supported more traditional Republican candidates. These developments combined to make Democrats and Republicans more similar than ever before in terms of ideological conceptualization in 2016.

Correlation methods within electronic structure theory focus on recovering the exact electron-electron interaction from the mean-field reference. For most chemical systems, including dynamic correlation, the correlation of the movement of electrons proves to be sufficient, yet exact methods for capturing dynamic correlation inherently scale polynomially with system size despite the locality of the electron cusp. This work explores a new family of methods for enhancing the locality of dynamic correlation methodologies with an aim toward improving accuracy and scalability. The introduction of range-separation into *ab initio* wavefunction methods produces short-range correlation methodologies, which can be supplemented with much faster approximate methods for long-range interactions.

First, I examine attenuation of second-order Møller-Plesset perturbation theory (MP2) in the aug-cc-pVDZ basis. MP2 treats electron correlation at low computational cost, but suffers from basis set superposition error (BSSE) and fundamental inaccuracies in long-range contributions. The cost differential between complete basis set (CBS) and small basis MP2 restricts system sizes where BSSE can be removed. Range-separation of MP2 could yield more tractable and/or accurate forms for short- and long-range correlation. Retaining only short-range contributions proves to be effective for MP2 in the small aug-cc-pVDZ (aDZ) basis. Using one range-separation parameter within either the complementary error function (erfc) or a sum of two error functions (terfc), superior behavior is obtained versus both MP2/aDZ and MP2/CBS for inter- and intra-molecular test sets. Attenuation of the long-range helps to cancel both BSSE and intrinsic MP2 errors. Direct scaling of the MP2 correlation energy (SMP2) proves useful as well. The resulting SMP2/aDZ, MP2(erfc, aDZ), and MP2(terfc, aDZ) methods perform far better than MP2/aDZ across systems with hydrogen-bonding, dispersion, and mixed interactions at a fraction of MP2/CBS computational cost.

Second, attenuated MP2 is developed within the larger aug-cc-pVTZ (aTZ) basis set for inter- and intramolecular non-bonded interactions. A single attenuation parameter is optimized on the S66 database of 66 intermolecular interactions, leading to a very large RMS error reduction by a factor of greater than 5 relative to standard MP2/aTZ. Attenuation introduces an error of opposite sign to basis set superposition error (BSSE) and overestimation of dispersion interactions in finite basis MP2. A variety of tests including the S22 set, conformer energies of peptides, alkanes, sugars, sulfate-water clusters, and the coronene dimer establish the transferability of the MP2(terfc, aTZ) model to other inter and intra-molecular interactions. Direct comparisons against attenuation in the smaller aug-cc-pVDZ basis shows that MP2(terfc, aTZ) often significantly outperforms MP2(terfc, aDZ), although at higher computational cost. MP2(terfc, aDZ) and MP2(terfc, aTZ) often outperform MP2 at the complete basis set limit. Comparison of the two attenuated MP2 models against each other and against attenuation using non-augmented basis sets gives insight into the error cancellation responsible for their remarkable success.

Third, I present an improved algorithm for single-node multi-threaded computation of the correlation energy using resolution of the identity second-order Møller-Plesset perturbation theory (RI-MP2). This algorithm is based on shared memory parallelization of the rate-limiting steps and an overall reduction in the number of disk reads. The requisite fifth-order computation in RI-MP2 calculations is efficiently parallelized within this algorithm, with improvements in overall parallel efficiency as the system size increases. Fourth-order steps are also parallelized. As an application, I present energies and timings for several large, noncovalently interacting systems with this algorithm, and demonstrate that the RI-MP2 cost is still typically less than 40% of the underlying self consistent field (SCF) calculation. The attenuated RI-MP2 energy is also implemented with this algorithm, and some new large-scale tests of this method are reported. The attenuated RI-MP2(terfc, aug-cc-pVDZ) method yields excellent agreement with benchmark values for the L7 database (R. Sedlak et al., J. Chem. Theory Comput. 2013, 9, 3364) and 10 tetrapeptide conformers (L. Goerigk et al., Phys. Chem. Chem. Phys. 2013, 15, 7028), with at least a 90% reduction in the root-mean-squared (RMS) error versus RI-MP2/aug-cc-pVDZ.

Fourth, semi-empirical spin-component scaled (SCS) attenuated MP2 is developed for treating both bonded and nonbonded interactions. SCS-MP2 improves the treatment of thermochemistry and noncovalent interactions relative to MP2, although the optimal scaling coefficients are quite different for thermochemistry versus noncovalent interactions. This work reconciles these two different scaling regimes for SCS-MP2 by using two different length scales for electronic attenuation of the two spin components. The attenuation parameters and scaling coefficients are optimized in the aug-cc-pVTZ (aTZ) basis using the S66 database of intermolecular interactions and the W4- 11 database of thermochemistry. Transferability tests are performed for atomization energies and barrier heights, as well as on further test sets for inter- and intramolecular interactions. SCS dual- attenuated MP2 in the aTZ basis, SCS-MP2(2terfc, aTZ), performs similarly to SCS-MP2/aTZ for thermochemistry while frequently outperforming MP2 at the complete basis set limit (CBS) for nonbonded interactions.

Finally, I examine the performance of attenuated MP2 for noncovalent interactions using basis sets that range as high as augmented triple (T) and quadruple (Q) zeta with TQ extrapolation towards the complete basis set (CBS) limit. By comparing training and testing performance as a function of basis set size, the effectiveness of attenuation as a function of basis set can be assessed. While attenuated MP2 with TQ extrapolation improves systematically over MP2, there are at most small improvements over attenuated MP2 in the aug-cc-pVTZ basis. Augmented functions are crucial for the success of attenuated MP2.

In this thesis, we present our work in pursuit of black-box, \textit{ab initio} methods for computing positions and widths of molecular resonances. The method of complex basis functions is efficiently implemented and applied in the context of various electronic structure approximations. Within the static exchange approximation, basis set effects are investigated and the method is applied to a series of N-containing hetercycles. The extension to Hartree-Fock theory allows for more accurate calculations. These methods have been applied to several small molecules, and the computation of properties within this framework is discussed. The application of complex basis functions to shape and Feshbach resonances at correlated levels of theory including M\o ller-Plesset perturbation theory at second order and equation of motion coupled cluster singles and doubles is also investigated from a practical perspective, and the prospect of using these methods for computing accurate potential energy surfaces is explored. Finally, we describe some theoretical and practical aspects of computing positions and widths of low-energy shape resonances by analytic continuation in the coupling constant. We find that the properties of attenuated Coulomb potentials make them ideal for such calculations.

Dynamic inter-electronic correlations are exquisitely local effects responsible for many interesting phenomena in molecular physics, including much or all of mutual attractions between molecules. The main thrust of this work is the development of high-accuracy, low-scaling models of electron correlation exploiting locality in the context of non-covalent interactions.

This thesis is concerned with the development of minimally-parameterized and highly-transferable density functionals. A methodology for searching a given functional space is developed and used to parameterize three novel functionals: ωB97X-V -- a 10-parameter, range-separated hybrid, generalized gradient approximation density functional with VV10 nonlocal correlation, B97M-V -- a 12-parameter, local meta-generalized gradient approximation density funcitonal with VV10 nonlocal correlation, and ωB97M-V -- a 12-parameter, range-separated hybrid, meta-generalized gradient approximation density functional with VV10 nonlocal correlation. These three functionals are validated by comparisons to the best existing density functionals in their class, and their proper usage (with respect to basis sets and integration grids) is documented to facilitate use in chemical applications.

With political campaigns becoming increasingly adversarial, scholars have recently given some much-needed attention to the impact of negative advertising on turnout.In a widely recognized Review article and subsequent book, Ansolabehere and his colleagues (1994, 1995) contend that attack advertising drives potential voters away from the polls. We dispute the generalizability of these claims outside of the experimental setting. Using NES survey data as well aggregate sources, we subject this previous research to rigorous real-world testing. The survey data directly contradict Ansolabehere et al.'s findings, yielding evidence of a turnout advantage for those recollecting negative presidential campaign advertising. In attempting to replicate Ansolabehere et al’s earlier aggregate results we uncover quite significant discrepancies and inconsistencies in their dataset. This analysis leads to the conclusion that their aggregate study is hopelessly flawed. We must conclude that attack advertising’s demobilization dangers are greatly exaggerated by Ansolabehere et al., while they completely miss negative political advertising’s turnout benefits -- at least in voters’ own context.

This dissertation examines whether, commensurate with the pattern of low voter turnout, people with disabilities also exhibit low levels of engagement across many types of political involvement. Then, given the engagement levels of people with disabilities, the dissertation explores the political implications for party politics in the United States. To do so, I conduct statistical analyses of data from the 2006 General Social Survey and the 2012 American National Election Study. In chapter 2, I show that having a disability is associated with an increased likelihood of being generally interested in politics and that people with disabilities are just as likely as people without a disability to follow the national news. I also show disability to be negatively associated with levels of political knowledge. In chapter 3, I find that, relative to people without disabilities, people with disabilities are similarly likely to feel politically efficacious and to engage in participatory activities aside from voting. In fact, having a disability is positively associated with contacting government officials. In chapter 4, I test hypotheses about people with disabilities identifying with the Democratic Party, having a liberal ideological orientation, and voting as such in recent general elections. I find support for these hypotheses and I also find that within the population of people with disabilities, Democratic Party identification is strongest among people with mobility-related disabilities. I conclude first by offering directions for future research. I also suggest that election administration officials could do more in terms of educational outreach to people with disabilities. Democratic Party officials would also find it in their interest to increase their outreach efforts to this segment of the population.

A radical molecule contains one or more electrons that are unpaired. A radicaloid may be defined as a molecule in which there are that are partially unpaired. As a result, the electronic structure of the radicaloid can be quite complicated for a variety of reasons. For a singlet biradicaloid, the singlet and triplet wavefunction can be quite close energetically which can lead to problems when trying to describe the system with a single determinant. The simplest solution to this problem is to allow the wavefunction to break spin-symmetry in order to get a lower energy. Unfortunately this action can lead to wavefunctions that are no longer eigenfunctions of the operator.

In the second chapter we investigate a distannyne which has a biradicaloid resonance structure. By examining the orbital Hessian, it is discovered that the spin-symmetric solution is a saddle-point in wavefunction space and is structurally different than the spin-polarized solution. We then increase the complexity of the model system and see that the spin-symmetric solution is only a minimum for the exact experimental system and not for a simplified model system in which bulky organic substituents are replaced by simpler phenyl groups. Therefore, the breaking of spin-symmetry is absolutely critical in the small model systems and the full substituents play a non-trivial role.

However, the breaking of the spin-symmetry can have consequences for physical quantities when correlated methods are used. At the point of spin polarization or unrestriction the orbital Hessian will have one eigenvalue which is zero. Since the relaxed density matrix in correlated methods like Second-Order M\o ller-Plesset theory (MP2) depend on the inverse of the Hessian, at the unrestriction point this quantity will be undefined. Some unphysical artifacts are identified as a direct consequence of this fact. First, discontinuities in first order molecular properties such as the dipole moment are seen at the geometries associated with unrestriction. Second, the relaxed density matrix itself fails to be N-representable, with natural orbital occupation numbers less than zero and greater than one. Therefore, it is desirable to use a method that is not dependent on the inverse of the Hessian like orbital optimized MP2 (O2).

Another system which requires the use of orbital optimization is a neutral soliton on a polyacetylene chain. In this system, the Hartree-Fock reference suffers from severe spin-polarization making the wavefunction physically unreasonable unless a very sophisticated treatment of electron correlation is used to correct this problem. Originally, it was found that computationally expensive methods like CCSD(T) and CASSCF could adequately describe small model chain but not the full system. The O2 method is found to be an dramatic improvement over traditional MP2 which can be feasibly applied to polyenyl chains long enough to characterize the soliton. It is also discovered that density functionals are generally inadequate in describing the half-width of the soliton.

Finally, the last chapter takes a slightly different perspective and focuses on the addition of correlation energy to a successful energy decomposition analysis based on absolutely localized molecular orbitals. It is discovered that the resulting new method can adequately describe systems with dispersive intermolecular interactions and large amounts of charge transfer. This scheme is then applied to the water dimer systems and it is found that all of the intermolecular interactions similar in size with the electrostatic interaction being the largest and the dispersive interaction being the smallest. This method is also contrasted with other EDA schemes.