Extension and applications of the GVVPT2 method to the study of transition metals

The ground and low-lying excited electronic states of molecules of the first ( 2 Sc , 2 Cr , 2 Mn , and 2 Ni ) and second ( 2 Y , 2 Mo , and 2 Tc ) row of transition elements have been investigated for the first time with the generalized Van Vleck second order multireference perturbation theory (GVVPT2) method, a variant of MRPT. All potential energy curves (PECs) obtained in these studies were smooth and continuous; that is, they are free from wiggles or inflexion points. In order to account for relativistic effects, which become important in heavy elements, the GVVPT2 method was extended to include scalar relativistic effects through the spin-free exact two component (sf-X2C) method and used in the studies of all molecules of second row transition elements and some of those of the first row considered in this present work. GVVPT2 studies of triatomic lithium and beryllium were also done as a first step to studies of small clusters of transition metals. The spectroscopic constants (bond lengths, harmonic frequencies, bond energies, and adiabatic transition energies) obtained for all PECs at the GVVPT2 level were in good agreement with experimental data, where available, and with results from previous studies using other high level ab initio methods. Optimized geometries of the triatomics were also in good agreement with previous findings. The studies included electronic states (e.g., the g 1 g 1 2 Σ and 3 Σ states of 2 Y as well as the g 5 1 Σ and g 9 1 Σ states of 2 Tc ) not previously discussed in the literature. As a first step to applying GVVPT2 to the study of relatively larger systems, the present work includes the results of efforts on improving DFT-in-DFT embedding theory. New equations were determined which involved an additional constraint of orthogonality of the orbitals of one subsystem to those of the complementary subsystem as warranted by formal arguments based on the formulation of DFT-in-DFT embedding. A computer program was realized using the new embedding equations and test calculations performed. Analyses of electron density deformations in embedding theory, in comparison with conventional Kohn-Sham (KS)-DFT densities, were performed using the new embedding program and a computer code that was also written to compute electron densities of molecules in real space, given reduced one particle density matrices. The results revealed that whereas the current formulation of DFT-in-DFT embedding theory generally underestimates electron density, at the interface between subsystems in comparison with conventional KS-DFT calculations of the supermolecule, the new DFT-in-DFT embedding scheme with the external orthogonality constraint was found to remedy the situation. Worthy of special note in this new embedding protocol is the fact that the nonadditive kinetic potential ( T v ), thought to be a major cause of weaknesses in DFT-in-DFT embedding and to which many previous research efforts have been devoted, can be set exactly to zero. The present work therefore realized, for the first time, a new DFT-in-DFT embedding theory that neither relies on kinetic functionals nor requires a supermolecular DFT calculation. Test calculations using the new embedding theory and supermolecular basis set expansion of KS orbitals reproduced conventional KS-DFT energies to at least the 7th decimal place (and even exactly at many geometries). A new way of expanding KS orbitals was also employed in the new embedding protocol, which is intermediate between the usual supermolecular and monomer basis expansions, referred to as the “extended monomer expansion”. The monomer basis expansion scheme was inadequate for the new DFT-in-DFT embedding protocol. Test calculations found this novel, computationally cheaper, extended monomer approach to give results quite close to those from supermolecular basis expansions

Cameroonian Immigrants Switching From Non-Stem To Stem-And-Related Fields In The United States

Recent studies on STEM education in the United States (U.S.) have largely focused on such issues as the ever increasing need for more STEM workers, STEM attrition/retention, the gender gap in STEM, encouraging more STEM enrollment both at college and post-graduate levels, and the use of modern technology to facilitate STEM education. Other studies have considered the impact of immigrants on STEM education in the U.S. and on the U.S. economy in terms of either creating or filling STEM jobs. Many of those studies underscore the importance of immigrants in boosting the high skilled, much needed, STEM labor force and thereby increasing the global competitiveness of the U.S. Despite a large volume of STEM-related research in the U.S., minimal research has focused on immigrants who enter the U.S. without prior STEM backgrounds and choose STEM or related majors while in the U.S. In particular, no prior study has considered Cameroonian immigrants with non-STEM majors and who switch into STEM or related fields upon arrival in the U.S. Such studies could unveil key factors that serve as strong motivators for STEM enrollment. To fill this gap, the present study investigated why Cameroonian immigrants who came into the U.S. without a prior STEM background switched into STEM or related fields while in the U.S. The study involved 8 Cameroonian immigrants who were majoring in either a STEM or related field who came into the U.S. without a prior STEM background. Data was obtained through in-depth, semi-structured, face-to-face, individual participant interviews. Participants attributed their failure to major in STEM while in Cameroon to the following: stereotypes, limited financial and other resources, negative influence from teachers, peers, relatives, and others, and the impact of non-STEM role models. Participants attributed their choice to switch into STEM or related fields while in the U.S. to job discrimination within non-STEM fields, ease of employment within STEM, and the impact of friends and others who directly encouraged them to switch. In comparing STEM education in Cameroon and the U.S., participants felt the U.S. offered many advantages such as increased flexibility, teacher accessibility, and financial and other resources. It was found that although participants had faced challenges upon switching into STEM in the U.S., their determination/resilience had led them to overcome those challenges and persist in their new majors. Overall, gender differences were insignificant in the decision to switch to a STEM or related major in the present study

Towards Better Management of Public Education in Cameroon: The Case for Decentralisation

This paper conceptualises centralisation and decentralisation and provides evidence that the Cameroon public education system is facing imminent decentralisation. It uses available literature and the author's teaching experience to criticise the centralised education system in Cameroon, especially in resource allocation and management. The author argues that to increase the quantity and quality of education in Cameroon, there is a need to decentralise responsibility for and control of education. He presents the model proposed by government for decentralisation and proposes roles and functions for the various levels of authority in the model. Résumé Cet article conceptualise les notions de centralisation et de décentralisation et démontre que le système éducatif camerounais va au devant d\'une décentralisation imminente. Il se base sur la littérature disponible à ce sujet, ainsi que sur l\'expérience pédagogique, pour critiquer la centralisation du système éducatif camerounais, particulièrement en matière de distribution et de gestion des ressources. L\'auteur avance que, pour améliorer la quantité et la qualité de l\'enseignement au Cameroun, il est indispensable de décentraliser l\'imputation et le contrôle y afférent. Il présente le modèle proposé par le gouvernement en vue de la décentralisation prévue, et suggère des rôles et fonctions pour les divers niveaux d\'autorité contenus dans le modèle. Africa Development/Afrique et développement Vol.XXIX, No 2, 2004: 134-15

Prevalence and factors associated with drug therapy problems among hypertensive patients at hypertension clinic of Mbarara Regional Referral Hospital, Uganda: a |cross-sectional study

Background: Despite the use of safe and effective conventional drugs, drug therapy problems (DTPs) pose a threat to the successful management of hypertension. DTPs are of a great concern in health care because of their serious consequences such as poor quality of life, increased health care costs, morbidity and mortality. However, there is no published information regarding the prevalence of DTPs and associated factors among hypertensive patients in Uganda. Objective: The aim of the study was to determine the prevalence and factors associated with DTPs among hypertensive patients at the hypertension clinic of Mbarara Regional Referral Hospital (MRRH). Method: A cross-sectional study was conducted at the hypertension clinic, MRRH, Uganda among 228 hypertensive patients. Data were collected from medical records using a data abstraction tool and patients were interviewed using a structured questionnaire. Data analysis was done using Statistical Package for Social Sciences (SPSS) version 22.0. Descriptive analysis was used to determine the prevalence of DTPs. Logistic regression was used to determine the association between the independent and dependent variables. Variables were considered statistically significant at p -value <0.05. Results: A total of 178 DTPs were identified among 141 hypertensive patients. The prevalence of antihypertensive-related DTPs was 61.8% (95% confidence interval [CI]: 55.3–67.5) with an average of 1.26 ± 0.52 DTPs per patient. Out of 141 participants with DTPs, 109 (77.3%) had one DTP, 27 (19.1%) had 2 DTPs, and 5 (3.5%) had 3 DTPs. The most common types of antihypertensive-related DTPs were ‘dosage too low’ which accounted for 53 (29.8%), followed by ‘adverse drug reactions’ which accounted for 48 (27%). Uncontrolled blood pressure (BP; adjusted odds ratio [AOR]: 4.17; 95% CI: 2.33–7.45, p  < 0.001) and routine laboratory test results (AOR: 1.87; 95% CI: 1.04–3.36, p  = 0.036) were significantly associated with antihypertensive-related DTPs among hypertensive patients. Conclusion: Almost two-thirds of study participants had antihypertensive-related DTPs. The most common DTPs were ‘dosage too low’ and ‘adverse drug reactions’ which both accounted for almost a third of the total DTPs each. Uncontrolled BP and routine laboratory test results were significantly associated with antihypertensive-related DTPs among the study participants. Our study emphasizes the need for improved patient care by clinical pharmacists to identify and prevent DTPs among hypertensive patients

Effect of Binding Geometry on Charge Transfer in CdSe Nanocrystals Functionalized by N719 Dyes to Tune Energy Conversion Efficiency

Semiconductor quantum dots (QDs) functionalized by metal–organic dyes show great promise in photocatalytic and photovoltaic applications. However, the charge transfer direction and rateskey processes governing the efficiency of energy conversionare strongly affected by the QD–dye interactions, insights on which are challenging to obtain experimentally. We use density functional theory (DFT) and constrained DFT calculations to investigate a degree of sensitivity of the electronic level alignment and related QD–dye electronic couplings to binding conformations of N719 dye at the surface of the 1.5 nm CdSe QD. Our calculations reveal a lack of direct correlations between the strength of the QD–dye interaction in terms of their binding conformations and the donor–acceptor electronic couplings. While the QD–dye binding conformations are the most stable when the N719 dye is attached to the QD via two carboxylate groups, the strongest electronic coupling between the QD as an electron donor and the dye as an electron acceptor is observed in structures bonded via the isocyanate ligands. Such strong electronic couplings also are responsible for significant stabilization of the dye’s occupied orbitals deep inside in the valence band of the QD making the hole transfer from the photoexcited QD to the dye thermodynamically unfavorable in structures bound via isocyanates. Our results suggest that the most probable binding conformations are those occurring via two carboxylate linkers, which exhibit very weak electronic couplings contributing to the electron transfer from the photoexcited CdSe QD to the N719 dye but provide the most favorable conditions for the hole transfer. Overall, our computational work provides an insightful view about the surface chemistry of CdSe regarding the donor–acceptor interaction, energy level alignment, and charge transfer between CdSe and dye molecule, which can guide the rational design of QD-based materials for energy conversion applications

Relativistic GVVPT2 Multireference Perturbation Theory Description of the Electronic States of Y₂ and Tc₂

The multireference generalized Van Vleck second-order perturbation theory (GVVPT2) method is used to describe full potential energy curves (PECs) of low-lying states of second-row transition metal dimers Y₂ and Tc₂, with scalar relativity included via the spin-free exact two-component (sf-X2C) Hamiltonian. Chemically motivated incomplete model spaces, of the style previously shown to describe complicated first-row transition metal diatoms well, were used and again shown to be effective. The studied states include the previously uncharacterized 2¹Σ_g⁺ and 3¹Σ_g⁺ PECs of Y₂. These states, together with 1¹Σ_g⁺, are relevant to discussion of controversial results in the literature that suggest dissociation asymptotes that violate the noncrossing rule. The ground state of Y₂ was found to be X⁵Σ_u^– (similar to Sc₂) with bond length <i>R</i>_e = 2.80 Å, binding energy <i>D</i>_e = 3.12 eV, and harmonic frequency ω_e = 287.2 cm^–1, whereas the lowest 1¹Σ_g⁺ state of Y₂ was found to lie 0.67 eV above the quintet ground state and had spectroscopic constants <i>R</i>_e = 3.21 Å, <i>D</i>_e = 0.91 eV, and ω_e = 140.0 cm^–1. Calculations performed on Tc₂ include study of the previously uncharacterized relatively low-lying 1⁵Σ_g⁺ and 1⁹Σ_g⁺ states (i.e., 0.70 and 1.84 eV above 1¹Σ_g⁺, respectively). The ground state of Tc₂ was found to be X³Σ_g^– with <i>R</i>_e = 2.13 Å, <i>D</i>_e = 3.50 eV, and ω_e = 336.6 cm^–1 (for the most stable isotope, Tc-98) whereas the lowest ¹Σ_g⁺ state, generally accepted to be the ground state symmetry for isovalent Mn₂ and Re₂, was found to lie 0.47 eV above the X³Σ_g^– state of Tc₂. The results broaden the range of demonstrated applicability of the GVVPT2 method