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1.
Teach Learn Med ; : 1-13, 2023 Aug 12.
Article in English | MEDLINE | ID: mdl-37571960

ABSTRACT

Phenomenon: Student-run free clinics (SRFCs) serve an integral role in most United States (US) medical schools and contribute substantially to literature on the quality of care to uninsured persons. There has been substantial growth over the past decade of scholarly work produced by SRFCs as they have increased in size and number. Research on patient care outcomes informs better care structures for patients, however there is no current synthesis of patient care outcomes research among SRFCs. This article provides an overview of SRFC research on patient outcomes to understand current research domains and to identify gaps in the literature. Approach: We completed a scoping review by searching Scopus, PubMed, and Journal of Student Run Clinics in June 2021. All peer-reviewed, English-language articles focused on patient-centered outcomes at SRFCs in the US were included. Two independent reviewers performed title, abstract, and full-text screening of relevant works, and eight reviewers conducted data extraction. Descriptive data analysis was performed along with relevant content analysis of patient-centered outcomes. Findings: The search strategy identified 784 studies, of which 87 met inclusion criteria. Most studies were published within the last six years (81.6%), located in California, New York, or Florida (43.7%), and intervention based (33.3%). Many studies (46.0%) had a specific disease of focus of which diabetes was the most researched(19.5%). Patient-centered studies were the leading focus of the study aims (40.2%), where key findings demonstrated primarily improved outcomes in clinic metrics post-intervention (36.8%) or equivalent/better clinical performance than national metrics (20.7%). Insights: This review brings to light gaps in the literature reporting research in SRFCs and can be applied to other low-resource settings. Future efforts to expand SRFC outcomes research should focus on community relationship building, understanding institutional support, and ensuring education on best practices for research within SRFCs. Doing so informs patient care improvement as SRFCs continue to operate as safety net clinics for marginalized populations.

2.
J Med Internet Res ; 25: e43873, 2023 05 03.
Article in English | MEDLINE | ID: mdl-36939670

ABSTRACT

BACKGROUND: Over 1 million people in the United States have died of COVID-19. In response to this public health crisis, the US Department of Health and Human Services launched the We Can Do This public education campaign in April 2021 to increase vaccine confidence. The campaign uses a mix of digital, television, print, radio, and out-of-home channels to reach target audiences. However, the impact of this campaign on vaccine uptake has not yet been assessed. OBJECTIVE: We aimed to address this gap by assessing the association between the We Can Do This COVID-19 public education campaign's digital impressions and the likelihood of first-dose COVID-19 vaccination among US adults. METHODS: A nationally representative sample of 3642 adults recruited from a US probability panel was surveyed over 3 waves (wave 1: January to February 2021; wave 2: May to June 2021; and wave 3: September to November 2021) regarding COVID-19 vaccination, vaccine confidence, and sociodemographics. Survey data were merged with weekly paid digital campaign impressions delivered to each respondent's media market (designated market area [DMA]) during that period. The unit of analysis was the survey respondent-broadcast week, with respondents nested by DMA. Data were analyzed using a multilevel logit model with varying intercepts by DMA and time-fixed effects. RESULTS: The We Can Do This digital campaign was successful in encouraging first-dose COVID-19 vaccination. The findings were robust to multiple modeling specifications, with the independent effect of the change in the campaign's digital dose remaining practically unchanged across all models. Increases in DMA-level paid digital campaign impressions in a given week from -30,000 to 30,000 increased the likelihood of first-dose COVID-19 vaccination by 125%. CONCLUSIONS: Results from this study provide initial evidence of the We Can Do This campaign's digital impact on vaccine uptake. The size and length of the Department of Health and Human Services We Can Do This public education campaign make it uniquely situated to examine the impact of a digital campaign on COVID-19 vaccination, which may help inform future vaccine communication efforts and broader public education efforts. These findings suggest that campaign digital dose is positively associated with COVID-19 vaccination uptake among US adults; future research assessing campaign impact on reduced COVID-19-attributed morbidity and mortality and other benefits is recommended. This study indicates that digital channels have played an important role in the COVID-19 pandemic response. Digital outreach may be integral in addressing future pandemics and could even play a role in addressing nonpandemic public health crises.


Subject(s)
COVID-19 , Adult , Humans , United States , COVID-19/epidemiology , COVID-19/prevention & control , COVID-19 Vaccines/therapeutic use , Pandemics , Health Promotion/methods , Vaccination , United States Dept. of Health and Human Services
3.
Nat Hum Behav ; 6(8): 1045-1047, 2022 08.
Article in English | MEDLINE | ID: mdl-35953595
4.
Molecules ; 27(5)2022 Mar 03.
Article in English | MEDLINE | ID: mdl-35268764

ABSTRACT

Interfacial interactions between liquid crystal (LC) and two-dimensional (2D) materials provide a platform to facilitate novel optical and electronic material properties. These interactions are uniquely sensitive to the local energy landscape of the atomically thick 2D surface, which can be strongly influenced by defects that are introduced, either by design or as a byproduct of fabrication processes. Herein, we present density functional theory (DFT) calculations of the LC mesogen 4-cyan-4'-pentylbiphenyl (5CB) on graphene in the presence of a monovacancy (MV-G). We find that the monovacancy strengthens the binding of 5CB in the planar alignment and that the structure is lower in energy than the corresponding homeotropic structure. However, if the molecule is able to approach the monovacancy homeotropically, 5CB undergoes a chemical reaction, releasing 4.5 eV in the process. This reaction follows a step-by-step process gradually adding bonds, inserting the 5CB cyano group into MV-G. We conclude that this irreversible insertion reaction is likely spontaneous, potentially providing a new avenue for controlling both LC behavior and graphene properties.

5.
Acta Crystallogr E Crystallogr Commun ; 77(Pt 4): 390-395, 2021 Apr 01.
Article in English | MEDLINE | ID: mdl-33936763

ABSTRACT

The title compound, C5D6ClN2O+·Cl-, crystallizes in the ortho-rhom-bic space group, Pbcm, and consists of a 4-chloro-2-methyl-6-oxo-3,6-di-hydro-pyrimidin-1-ium cation and a chloride anion where both moieties lie on a crystallographic mirror. The cation is disordered and was refined as two equivalent forms with occupancies of 0.750 (4)/0.250 (4), while the chloride anion is triply disordered with occupancies of 0.774 (12), 0.12 (2), and 0.11 (2). Unusually, the bond angles around the C=O unit range from 127.2 (6) to 115.2 (3)° and similar angles have been found in other structures containing a 6-oxo-3,6-di-hydro-pyrimidin-1-ium cation, including the monclinic polymorph of the title compound, which crystallizes in the monoclinic space group P21/c [Kawai et al. (1973 ▸). Cryst. Struct. Comm. 2, 663-666]. The cations and anions pack into sheets in the ab plane linked by N-H⋯Cl hydrogen bonds as well as C-H⋯O and Cl⋯O inter-actions. In graph-set notation, these form R 3 3(11) and R 3 2(9) rings. Theoretical calculations seem to indicate that the reason for the unusual angles at the sp 2 C is the electrostatic inter-action between the oxygen atom and the adjacent N-H hydrogen.

6.
J Urol ; 205(6): 1733-1739, 2021 Jun.
Article in English | MEDLINE | ID: mdl-33605791

ABSTRACT

PURPOSE: In men, complaints of nocturia causing poor sleep are often attributed to benign prostatic hyperplasia and treated with benign prostatic hyperplasia medications. We assessed whether treating lower urinary tract symptoms with dutasteride altered either nocturia or sleep quality using data from REDUCE. MATERIALS AND METHODS: REDUCE was a 4-year randomized, multicenter trial comparing dutasteride 0.5 mg/day vs placebo for prostate cancer chemoprevention. Study participants were men considered at increased risk for prostate cancer. Eligibility included age 50-75 years, prostate specific antigen 2.5-10 ng/ml, and 1 negative prostate biopsy. At baseline, 2 years and 4 years, men completed the International Prostate Symptom Score and Medical Outcomes Study Sleep Scale, a 6-item scale assessing sleep. To test differences in nocturia and Medical Outcomes Study Sleep Scale over time, we used linear mixed models adjusted for baseline confounders. Subanalyses were conducted in men symptomatic from lower urinary tract symptoms, nocturia, poor sleep, or combinations thereof. RESULTS: Of 6,914 men with complete baseline data, 80% and 59% were assessed at 2 and 4-year followup, respectively. Baseline characteristics were balanced between treatment arms. Dutasteride improved nocturia at 2 (-0.15, 95% CI -0.21, -0.09) and 4 years (-0.24, 95% CI -0.31, -0.18) but did not improve sleep. When limited to men symptomatic from lower urinary tract symptoms, nocturia, poor sleep or combinations thereof, results mirrored findings from the full cohort. CONCLUSIONS: In men with poor sleep who complain of nocturia, treatment of lower urinary tract symptoms with dutasteride modestly improves nocturia but has no effect on sleep. These results suggest men with poor sleep who complain of nocturia may not benefit from oral benign prostatic hyperplasia treatment.


Subject(s)
5-alpha Reductase Inhibitors/therapeutic use , Dutasteride/therapeutic use , Lower Urinary Tract Symptoms/complications , Lower Urinary Tract Symptoms/drug therapy , Nocturia/drug therapy , Nocturia/etiology , Sleep , Humans , Male , Middle Aged , Nocturia/physiopathology , Treatment Outcome
7.
Nat Hum Behav ; 4(12): 1236-1244, 2020 12.
Article in English | MEDLINE | ID: mdl-32958902

ABSTRACT

Local news outlets have struggled to stay open in the more competitive market of digital media. Some have noted that this decline may be due to the ways in which digital platforms direct attention to some news outlets and not others. To test this theory, we collected 12.29 million responses to Google News searches within all US counties for a set of keywords. We compared the number of local outlets reported in the results against the number of national outlets. We find that, unless consumers are searching specifically for topics of local interest, national outlets dominate search results. Features correlated with local supply and demand, such as the number of local outlets and demographics associated with local news consumption, are not related to the likelihood of finding a local news outlet. Our findings imply that platforms may be diverting web traffic and desperately needed advertising dollars away from local news.


Subject(s)
Internet , Mass Media , Social Media , Algorithms , Humans , Models, Theoretical
8.
J Chem Theory Comput ; 16(10): 6418-6427, 2020 Oct 13.
Article in English | MEDLINE | ID: mdl-32808780

ABSTRACT

Computational simulation of nonadiabatic molecular dynamics is an indispensable tool for understanding complex photoinduced processes such as internal conversion, energy transfer, charge separation, and spatial localization of excitons, to name a few. We report an implementation of the fewest-switches surface-hopping algorithm in the NWChem computational chemistry program. The surface-hopping method is combined with linear-response time-dependent density functional theory calculations of adiabatic excited-state potential energy surfaces. To treat quantum transitions between arbitrary electronic Born-Oppenheimer states, we have implemented both numerical and analytical differentiation schemes for derivative nonadiabatic couplings. A numerical approach for the time-derivative nonadiabatic couplings together with an analytical method for calculating nonadiabatic coupling vectors is an efficient combination for surface-hopping approaches. Additionally, electronic decoherence schemes and a state reassigned unavoided crossings algorithm are implemented to improve the accuracy of the simulated dynamics and to handle trivial unavoided crossings. We apply our code to study the ultrafast decay of photoexcited benzene, including a detailed analysis of the potential energy surface, population decay timescales, and vibrational coordinates coupled to the excitation dynamics. We also study the photoinduced dynamics in trans-distyrylbenzene. This study provides a baseline for future implementations of higher-level frameworks for simulating nonadiabatic molecular dynamics in NWChem.

9.
J Phys Chem B ; 123(26): 5536-5544, 2019 07 05.
Article in English | MEDLINE | ID: mdl-31180658

ABSTRACT

Using a large set of ab initio molecular dynamics trajectories we demonstrate that the mechanistic details of aqueous proton diffusion are insensitive to finite size effects. Furthermore, we show how correlation in the proton hopping direction is related to the presolvation of the hydronium ion. Specifically, we observe a dependence of the probability for the excess proton to return to its previous hydronium ion on whether that hydronium ion was accepting a hydrogen bond from a fourth water molecule at the time the excess proton left. The dynamics of this fourth water molecule was previously linked to the net displacement of the proton, and our analysis shows that this connection is due to the changes in the hopping probability that we calculate. Additionally, we show how our simulated dynamics with correlations that imply a faster time scale are compatible with recent spectroscopy results that point to a slower hopping time scale by looking closely at which proton transitions are being taken into consideration. Finally, we show that the correlation in proton hopping directions is not strongly influenced by interactions among hydronium ions.

10.
Phys Rev E ; 100(6-1): 062701, 2019 Dec.
Article in English | MEDLINE | ID: mdl-31962509

ABSTRACT

We present ground-state electronic properties of the liquid crystal 4-cyano-4^{'}-pentylbiphenyl (5CB) on the two-dimensional materials monolayer graphene, hexagonal boron nitride, and phosphorene. Our density functional theory results show that the physisorption is robust on all surfaces with the strongest binding of 5CB on phosphorene. All surfaces exhibit flexural distortion, especially monolayer graphene and hexagonal boron nitride. While we find type-I alignment for all three substrates, meaning the Fermi level of the system is in the HOMO-LUMO gap of 5CB, the band structures are qualitatively different. Unlike for graphene and phosphorene, the HOMO-LUMO of 5CB appear as localized states within the band gap of boron nitride. In addition, we find that the valence band for boron nitride is sensitive to the orientation of 5CB relative to the surface. The qualitatively different band structures demonstrate the importance of substrate selection for tailoring the electronic and optoelectronic properties of nematic liquid crystals on two-dimensional materials.

11.
Chem Sci ; 9(35): 7126-7132, 2018 Sep 21.
Article in English | MEDLINE | ID: mdl-30310634

ABSTRACT

The aqueous proton displays an anomalously large diffusion coefficient that is up to 7 times that of similarly sized cations. There is general consensus that the proton achieves its high diffusion through the Grotthuss mechanism, whereby protons hop from one molecule to the next. A main assumption concerning the extraction of the timescale of the Grotthuss mechanism from experimental results has been that, on average, there is an equal probability for the proton to hop to any of its neighboring water molecules. Herein, we present ab initio simulations that show this assumption is not generally valid. Specifically, we observe that there is an increased probability for the proton to revert back to its previous location. These correlations indicate that the interpretation of the experimental results need to be re-examined and suggest that the timescale of the Grotthuss mechanism is significantly shorter than was previously thought.

12.
Inorg Chem ; 57(9): 4921-4925, 2018 May 07.
Article in English | MEDLINE | ID: mdl-29688716

ABSTRACT

Orange crystals of a Sn14 cluster have been isolated in up to 22% yield from a reaction between Me3SiCH2SnCl3, SnCl4, and LiAlH4. The structure determined by single crystal X-ray diffraction shows three unique Sn atoms in a 6:6:2 ratio, with all Sn atoms 4-coordinate, similar to the tetrahedral bonding in elemental gray Sn. The solid state 117Sn MAS NMR spectrum shows the three types of distinct Sn atoms in the expected 3:3:1 intensity ratio with respective chemical shifts of 87.9, -66.6, and -607.1 ppm relative to Me4Sn. The chemical shift of the two Sn atoms without ligands (bonded only to Sn), at -607.1 ppm, is the most upfield, and is the closest to the chemical shift, reported here, of bulk gray tin (-910 ppm). First-principles density functional theory calculations of the chemical shielding tensors corroborate this assignment. While the core coordination is distorted from the ideal tetrahedral arrangement in the diamond structure of gray tin, this Sn14 cluster, as the largest reported cluster with all 4-coordinate Sn, represents a major incremental step toward being able to prepare atomically precise nanoparticles of gray tin.

13.
Phys Chem Chem Phys ; 19(40): 27452-27462, 2017 Oct 18.
Article in English | MEDLINE | ID: mdl-28975162

ABSTRACT

Three meso-substituted tetrapyridyl porphyrins (free base, Ni(ii), and Cu(ii)) were investigated for their optical limiting (OL) capabilities using real-time (RT-), linear-response (LR-), and quadratic-response (QR-) time-dependent density functional theory (TDDFT) methods. These species are experimentally known to display a prominent reverse saturable absorption feature between the Q and B bands of the ground-state absorption (GSA), which has been attributed to increased excited-state absorption (ESA) relative to GSA. A recently developed RT-TDDFT based method for calculating ESA from a LR-TDDFT density was utilized with eight exchange-correlation functionals (BLYP, PBE, B3LYP, CAM-B3LYP, PBE0, M06, BHLYP, and BHandH) and contrasted with calculations of ESA using QR-TDDFT with five exchange-correlation functionals (BLYP, B3LYP, CAM-B3LYP, BHLYP, and BHandH). This allowed for comparison between functionals with varying amounts of exact exchange as well as between the ability of RT-TDDFT and QR-TDDFT to reproduce OL behavior in porphyrin systems. The absorption peak positions and intensities for GSA and ESA are significantly impacted by the choice of DFT functional, with the most critical factor identified as the amount of exact exchange in the functional form. Calculating ESA with QR-TDDFT is found to be significantly more sensitive to the amount of exact exchange than GSA and ESA with RT-TDDFT, as well as GSA with LR-TDDFT. An analogous behavior is also demonstrated for the polycyclic aromatic hydrocarbon coronene. This is problematic when using the same approximate functional for calculation of both GSA and ESA, as the LR- and QR-TDDFT excitation energies will not have similar errors. Overall, the RT-TDDFT method with hybrid functionals reproduces the OL features for the porphyrin systems studied here and is a viable computational approach for efficient screening of molecular complexes for OL properties.

14.
J Phys Chem A ; 121(6): 1344-1350, 2017 Feb 16.
Article in English | MEDLINE | ID: mdl-28117998

ABSTRACT

Recent developments in nanophotonics have paved the way for achieving significant advances in the realm of single-molecule chemical detection, imaging, and dynamics. In particular, surface-enhanced Raman scattering (SERS) is a powerful analytical technique that is now routinely used to identify the chemical identity of single molecules. Understanding how nanoscale physical and chemical processes affect single-molecule SERS spectra and selection rules is a challenging task and is still actively debated. Herein, we explore underappreciated chemical phenomena in ultrasensitive SERS. We observe a fluctuating excited electronic state manifold, governed by the conformational dynamics of a molecule (4,4'-dimercaptostilbene, DMS) interacting with a metallic cluster (Ag20). This affects our simulated single-molecule SERS spectra; the time trajectories of a molecule interacting with its unique local environment dictates the relative intensities of the observable Raman-active vibrational states. Ab initio molecular dynamics of a model Ag20-DMS system are used to illustrate both concepts in light of recent experimental results.

15.
Sci Adv ; 2(4): e1501630, 2016 Apr.
Article in English | MEDLINE | ID: mdl-27152346

ABSTRACT

Ice-nucleating organisms play important roles in the environment. With their ability to induce ice formation at temperatures just below the ice melting point, bacteria such as Pseudomonas syringae attack plants through frost damage using specialized ice-nucleating proteins. Besides the impact on agriculture and microbial ecology, airborne P. syringae can affect atmospheric glaciation processes, with consequences for cloud evolution, precipitation, and climate. Biogenic ice nucleation is also relevant for artificial snow production and for biomimetic materials for controlled interfacial freezing. We use interface-specific sum frequency generation (SFG) spectroscopy to show that hydrogen bonding at the water-bacteria contact imposes structural ordering on the adjacent water network. Experimental SFG data and molecular dynamics simulations demonstrate that ice-active sites within P. syringae feature unique hydrophilic-hydrophobic patterns to enhance ice nucleation. The freezing transition is further facilitated by the highly effective removal of latent heat from the nucleation site, as apparent from time-resolved SFG spectroscopy.


Subject(s)
Bacteria/metabolism , Bacterial Outer Membrane Proteins/metabolism , Pseudomonas syringae/metabolism , Bacteria/chemistry , Hydrogen Bonding , Ice , Molecular Dynamics Simulation , Plants/microbiology , Pseudomonas syringae/pathogenicity , Temperature , Water/metabolism
16.
J Phys Chem Lett ; 7(7): 1387-91, 2016 Apr 07.
Article in English | MEDLINE | ID: mdl-27007445

ABSTRACT

Optical-limiting materials are capable of attenuating light to protect delicate equipment from high-intensity light sources. Phthalocyanines have attracted a lot of attention for optical-limiting applications due to their versatility and large nonlinear absorption. With excited-state absorption (ESA) being the primary mechanism for optical limiting behavior in phthalocyanines, the ability to tune the optical absorption of ground and excited states in phthalocyanines would allow for the development of advanced optical limiters. We recently developed a method for the calculation of ESA based on real-time time-dependent density functional theory propagation of an excited-state density. In this work, we apply the approach to zinc phthalocyanine, demonstrating the ability of our method to efficiently identify the optical limiting potential of a molecular complex.

17.
J Phys Chem A ; 120(4): 556-61, 2016 Feb 04.
Article in English | MEDLINE | ID: mdl-26752240

ABSTRACT

Simulating the spectroscopic properties of short-lived thermal and photochemical reaction intermediates and products is a challenging task, as these species often feature atypical molecular and electronic structures. The complex environments in which such species typically reside in practice add further complexity to the problem. Herein, we tackle this problem in silico using ab initio molecular dynamics (AIMD) simulations, employing iso-CHBr3, namely H(Br)C-Br-Br, as a prototypical system. This species was chosen because it features both a nonconventional C-Br-Br bonding pattern, as well as a strong dependence of its spectral features on the local environment in which it resides, as illustrated in recent experimental reports. We simulate the UV-vis and IR spectra of iso-CHBr3 in the gas phase, as well as in a Ne cluster (64 atoms) and in a methylcyclohexane cage (14 solvent molecules) representative of the previously characterized matrix isolated and solvated iso-CHBr3 species. We exclusively perform fully quantum mechanical static and dynamic simulations. By comparing our condensed phase simulations to their experimental analogues, we stress the importance of (i) conformational sampling, even at cryogenic temperatures, and (ii) using a fully quantum mechanical description of both solute and bath to properly account for the experimental observables.

18.
BJU Int ; 118(2): 250-7, 2016 08.
Article in English | MEDLINE | ID: mdl-26351095

ABSTRACT

OBJECTIVE: To determine whether there are subsets of men with pathological high grade prostate cancer (Gleason score 8-10) with particularly high or low 2-year biochemical recurrence (BCR) risk after radical prostatectomy (RP) when stratified into groups based on combinations of pathological features, such as surgical margin status, extracapsular extension (ECE) and seminal vesicle invasion (SVI). MATERIALS AND METHODS: We identified 459 men treated with RP with pathological Gleason score 8-10 prostate cancer in the SEARCH database. The men were stratified into five groups based on pathological characteristics: group 1, men with negative surgical margins (NSMs) and no ECE; group 2, men with positive surgical margin (PSMs) and no ECE; group 3, men with NSMs and ECE; group 4, men with PSMs and ECE; and group 5, men with SVI. Cox proportional hazards models and the log-rank test were used to compare BCR among the groups. RESULTS: At 2 years after RP, pathological group was significantly correlated with BCR (log-rank, P < 0.001) with patients in group 5 (+SVI) having the highest BCR risk (66%) and those in group 1 (NSMs and no ECE) having the lowest risk (14%). When we compared groups 2, 3, and 4, with each other, there was no significant difference in BCR among the groups (~50% 2-year BCR risk; log-rank P = 0.28). Results were similar when adjusting for prostate-specific antigen, age, pathological Gleason sum and clinical stage, or after excluding men who received adjuvant therapy. CONCLUSIONS: In patients with high grade (Gleason score 8-10) prostate cancer after RP, the presence of either PSMs, ECE or SVI was associated with an increased risk of early BCR, with a 2-year BCR risk of ≥50%. Conversely, men with organ-confined margin-negative disease had a very low risk of early BCR despite Gleason score 8-10 disease.


Subject(s)
Prostatic Neoplasms/pathology , Aged , Databases, Factual , Humans , Male , Middle Aged , Neoplasm Grading , Prostatic Neoplasms/surgery , Retrospective Studies , Treatment Outcome
19.
J Phys Chem B ; 120(8): 1429-36, 2016 Mar 03.
Article in English | MEDLINE | ID: mdl-26222601

ABSTRACT

Carbon-hydrogen (C-H) vibration modes serve as key probes in the chemical identification of hydrocarbons and in vibrational sum-frequency generation spectroscopy of hydrocarbons at the liquid/gas interface. Their assignments pose a challenge from a theoretical viewpoint. In this work, we present a detailed study of the C-H stretching region of dimethyl sulfoxide using a new ab initio molecular dynamics (AIMD) module that we have implemented in NWChem. Through a combination of AIMD simulations and static normal mode analysis, we interpret experimental infrared and Raman spectra and explore the role of anharmonic effects in this system. Comprehensive anharmonic normal mode analysis of the C-H stretching region casts doubt upon previous experimental assignments of the shoulder on the symmetric C-H stretching peak. In addition, our AIMD simulations also show significant broadening of the in-phase symmetric C-H stretching resonance, which suggests that the experimentally observed shoulder is due to thermal broadening of the symmetric stretching resonance.

20.
J Chem Theory Comput ; 11(9): 4294-303, 2015 Sep 08.
Article in English | MEDLINE | ID: mdl-26575924

ABSTRACT

The optical response of excited states is a key property used to probe photophysical and photochemical dynamics. Additionally, materials with a large nonlinear absorption cross-section caused by two-photon (TPA) and excited state absorption (ESA) are desirable for optical limiting applications. The ability to predict the optical response of excited states would help in the interpretation of transient absorption experiments and aid in the search for and design of optical limiting materials. We have developed an approach to obtain excited state absorption spectra by combining real-time (RT) and linear-response (LR) time-dependent density functional theory (TDDFT). Being based on RT-TDDFT, our method is aimed at tackling larger molecular complexes and materials systems where excited state absorption is predominantly seen and many time-resolved experimental efforts are focused. To demonstrate our method, we have calculated the ground and excited state spectra of H2⁺ and H2 due to the simplicity in the interpretation of the spectra. We have validated our new approach by comparing our results for butadiene with previously published results based on quadratic response (QR). We also present results for oligofluorenes, where we compare our results with both QR-TDDFT and experimental measurements. Because our method directly measures the response of an excited state, stimulated emission features are also captured; although, these features are underestimated in energy which could be attributed to a change of the reference from the ground to the excited state.

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