RESUMEN
The electron correlation energy in a chemical system is defined as a difference between the energy of an exact energy for a given Hamiltonian, and a mean-field, or single determinant, approximation to it. A promising way to model electron correlation is through the expectation value of a linear two-electron operator for the Kohn-Sham single determinant wavefunction. For practical reasons, it is desirable for such an operator to be universal, i.e., independent of the positions and types of nuclei in a molecule. The correlation operator models the effect of electron correlation on the interaction energy in a electron pair. We choose an operator expanded in a small number of Gaussians as a model for electron correlation, and test it by computing atomic and molecular adiabatic excited states. The computations are performed within the Δ Self-Consistent Field (ΔSCF) formalism, and are compared to the time-dependent density functional theory model with popular density functionals. The simplest form of the correlation operator contains only one parameter derived from the helium atom ground state correlation energy. The correlation operator approach significantly outperforms other methods in computation of atomic excitation energies. The accuracy of molecular excitation energies computed with the correlation operator is limited by the shortcomings of the ΔSCF methodology in describing excited states.
RESUMEN
INTRODUCTION: There is a lack of quantitative data on healthcare professionals' (HCPs) time dedicated to nebulized chronic obstructive pulmonary disease (COPD) therapy in inpatient and long-term care (LTC) settings. Using time and motion methodology, we quantified HCP time and opportunity costs (time and materials) associated with nebulized COPD therapy in inpatient and LTC settings and estimated efficiencies of changing to once-daily therapy. METHODS: A case report form was built to reflect local nebulization workflow. Primary outcomes were mean active HCP time per predefined task and mean total active HCP time associated with short-acting beta agonist (SABA) and SABA/short-acting muscarinic antagonist (SAMA) combination nebulization processes. RESULTS: Twenty observations occurred within each setting. Inpatient observations included three SABA and 17 SABA/SAMA (from 18 different patients), and LTC observations included five SABA and 15 SABA/SAMA (from eight different patients). Mean total process time was 16.12 min in the inpatient setting (95% CI 14.48-17.76) and 21.0 min in the LTC setting (95% CI 18.8-23.2), with the actual nebulization comprising over 50% of process time for both. In LTC, CIs suggest a difference by cognitive impairment status: mean 24.1 min (95% CI 21.3-26.9) if cognitively impaired versus 19.0 min (95% CI 16.1-21.8) if not. In the inpatient setting, the estimated process time/admission was 7.8 h; a once-daily nebulized drug would require only 2.3 h. In LTC, the estimated process time was 32.1 h/month; a once-daily nebulized drug would require only 13.7 h/month. Estimated nebulization cost was $243/admission for current versus $72 for once-daily dosing in inpatient, and $1177/month versus $504 in LTC. CONCLUSIONS: The nebulization process for COPD patients in both inpatient and LTC settings consumes considerable HCP time. A switch from SABA or SABA/SAMA to a drug with a once-daily nebulization frequency could generate substantial time savings depending on the setting and site characteristics.