Showing papers by "Thomas Kjærgaard published in 2009"

Quasienergy formulation of damped response theory.

Abstract: We present a quasienergy-based formulation of damped response theory where a common effective lifetime parameter has been introduced for all excited states in terms of complex excitation energies. The introduction of finite excited state lifetimes leads to a set of (complex) damped response equations, which have the same form to all orders in the perturbation. An algorithm is presented for solving the damped response equations in Hartree-Fock theory and Kohn-Sham density functional theory. The use of the quasienergy formulation allows us to obtain directly the computationally simplest expressions for damped response functions by applying a set of response parameter elimination rules, which minimize the total number of damped response equations to be solved. In standard response theory broadened absorption spectra are obtained by ad hoc superimposing lineshape functions onto the absorption stick spectra, whereas an empirical lineshape function common to all excitations is an integrated part of damped response theory. By superimposing the lineshape functions inherent in damped response theory onto the stick spectra of standard response theory, we show that the absorption spectra obtained in standard and damped response theory calculations are identical. We demonstrate that damped response theory may be applied to obtain absorption spectra in all frequency ranges, also those that are not readily addressed using standard response theory. This makes damped response theory an effective tool, e.g., for determining absorption spectra for large molecules, where the density of the excited states may be very high, and where standard response theory therefore is not applicable in practice. A thorough comparison is given between our formulation of damped response theory and the formulation by Norman et al. [J. Chem. Phys. 123, 194103 (2005)].

Relation of nasal air flow to nasal cavity dimensions.

Abstract: Objective: To investigate the relationship between nasal cavity dimensions and airflow based on measures of acoustic rhinometry (AR) and peak nasal inspiratory flow (PNIF) in a very large sample of mixed rhinologic and nonrhinologic patients. Design: Clinical survey conducted between 2001 and 2007. Setting: Secondary referral ambulatory center and hospital. Patients: The study population comprised 2523 consecutive adult patients, mainly white, referred to the Department of Otolaryngology–Head and Neck Surgery, Sorlandet Hospital, Kristiansand, Norway, for evaluation of sleep-related disorders (eg, snoring, sleep apnea) or chronic nasal complaints. Intervention: The subjects underwent AR and PNIF at baseline and after decongestion of the nasal mucosa with xylometazoline hydrochloride. Questionnaires and height and weight measurements were obtained prior to the nasal recordings. Main Outcome Measure: Associations between measures of AR (volume and area) and PNIF. Results: Nearly linear relationships were found between PNIF in 4 categories and nasal cavity volumes and minimal cross-sectional areas (analysis of variance, P.001; post hoc analysis, P.01). Adjusted associations between 5 of 6 AR measures and PNIF both at baseline and after decongestion were significant (P.001 in 9 cases and P=.03 in 1 case). Conclusions: Our study indicates statistically significant associations between nasal cavity dimensions and PNIF. The most important structural determinant for PNIF is the minimal cross-sectional area of the nasal cavity.

Gauge-Origin Independent Formulation and Implementation of Magneto-Optical Activity within Atomic-Orbital-Density Based Hartree-Fock and Kohn-Sham Response Theories

Abstract: A Lagrangian approach has been used to derive gauge-origin independent expressions for two properties that rationalize magneto-optical activity, namely the Verdet constant V(ω) of the Faraday effect and the ℬ term of magnetic circular dichroism. The approach is expressed in terms of an atomic-orbital density-matrix based formulation of response theory and use London atomic orbitals to parametrize the magnetic field dependence. It yields a computational procedure which is both gauge-origin independent and suitable for linear-scaling at the level of time-dependent Hartree-Fock and density functional theory. The formulation includes a modified preconditioned conjugated gradient algorithm, which projects out the excited state component from the solution to the linear response equation. This is required when solving one of the response equations for the determination of the ℬ term and divergence is encountered if this component is not projected out. Illustrative results are reported for the Verdet constant of H2, HF, CO, N2O, and CH3CH2CH3 and for the ℬ term of pyrimidine, phosphabenzene, and pyridine. The results are benchmarked against gauge-origin independent CCSD values.