Assessing the importance of multireference correlation in predicting reversed conductance decay.

In a classical electronic resistor, conductance decays as the device length increases according to Ohm's Law. While most molecular series display a comparable exponential decay in conductance with increasing molecular length, a class of single-molecule device series exists where conductance instead increases with molecular/device length, a phenomenon called reversed conductance decay. While reversals of conductance decay have been repeatedly theoretically predicted, they have been far more difficult to demonstrate experimentally. Previous studies have suggested that theoretical multi-reference(static) correlation errors may be a major cause of this discrepancy, yet most single-molecule transport methods are unable to treat multireference correlation. Using our unique multireference transport method based on non-equilibrium Green's function and multiconfigurational pair-density functional theory (NEGF-MCPDFT), we examined a previously predicted case of reversed conductance decay in systems of linear chains of phenyl rings with varying lengths and electrode designs. We compare our NEGF-MCPDFT results to those of non-multireference NEGF methods to quantify the exact role of static correlation in conductance decay reversals and clarify their relative importance to geometric and electrode design/coupling considerations.

A multiconfiguration pair-density functional theory-based approach to molecular junctions.

Due to their small size and unique properties, single-molecule electronics have long seen research interest from experimentalists and theoreticians alike. From a theoretical standpoint, modeling these systems using electronic structure theory can be difficult due to the importance of electron correlation in the determination of molecular properties, and this electron correlation can be computationally expensive to consider, particularly multiconfigurational correlation energy. In this work, we develop a new approach for the study of single-molecule electronic systems, denoted NEGF-MCPDFT, which combines multiconfiguration pair-density functional theory (MCPDFT) with the non-equilibrium Green's function formalism (NEGF). The use of MCPDFT with NEGF allows for the efficient inclusion of both static and dynamic electron correlations in the description of the junction's electronic structure. Complete active space self-consistent field wave functions are used as references in the MCPDFT calculation, and as with any active space method, effort must be made to determine the proper orbital character to include in the active space. We perform conductance and transmission calculations on a series of alkanes (predominantly single-configurational character) and benzyne (multiconfigurational character), exploring the role that active space selection has on the computed results. For the alkane junctions explored (where dynamic electron correlation dominates), the MCPDFT-NEGF results agree well with the DFT-NEGF results. For the benzyne junction (which has a significant static correlation), we see clear differences in the MCPDFT-NEGF and DFT-NEGF results and evidence that NEGF-MCPDFT is capturing additional electron correlation effects beyond those provided by the Perdew-Burke-Ernzerhof functional.

Acetyl nitrate mediated conversion of methyl ketones to diverse carboxylic acid derivatives.

The development of a novel acetyl nitrate mediated oxidative conversion of methyl ketones to carboxylic acid derivatives is described. By analogy to the haloform reaction and supported by experimental and computational investigation we propose a mechanism for this transformation.

Development and application of a 2-electron reduced density matrix approach to electron transport via molecular junctions.

Can an electronic device be constructed using only a single molecule? Since this question was first asked by Aviram and Ratner in the 1970s [Chem. Phys. Lett. 29, 277 (1974)], the field of molecular electronics has exploded with significant experimental advancements in the understanding of the charge transport properties of single molecule devices. Efforts to explain the results of these experiments and identify promising new candidate molecules for molecular devices have led to the development of numerous new theoretical methods including the current standard theoretical approach for studying single molecule charge transport, i.e., the non-equilibrium Green's function formalism (NEGF). By pairing this formalism with density functional theory (DFT), a wide variety of transport problems in molecular junctions have been successfully treated. For some systems though, the conductance and current-voltage curves predicted by common DFT functionals can be several orders of magnitude above experimental results. In addition, since density functional theory relies on approximations to the exact exchange-correlation functional, the predicted transport properties can show significant variation depending on the functional chosen. As a first step to addressing this issue, the authors have replaced density functional theory in the NEGF formalism with a 2-electron reduced density matrix (2-RDM) method, creating a new approach known as the NEGF-RDM method. 2-RDM methods provide a more accurate description of electron correlation compared to density functional theory, and they have lower computational scaling compared to wavefunction based methods of similar accuracy. Additionally, 2-RDM methods are capable of capturing static electron correlation which is untreatable by existing NEGF-DFT methods. When studying dithiol alkane chains and dithiol benzene in model junctions, the authors found that the NEGF-RDM predicts conductances and currents that are 1-2 orders of magnitude below those of B3LYP and M06 DFT functionals. This suggests that the NEGF-RDM method could be a viable alternative to NEGF-DFT for molecular junction calculations.

State of the Art: Reconstructing Partial Mastectomy Defects with Autologous Fat Grafting.

It is estimated that more than 231,840 new cases of invasive breast cancers will be diagnosed in 2015. Many of these patients will be treated with lumpectomy and radiation or with mastectomy. Historically less than 25 percent of patients undergo immediate breast reconstruction, and autologous fat grafting represents a technique to help address some of the difficulties encountered in delayed reconstruction. The use of autologous fat grafting for reconstruction of soft-tissue defects is an increasingly common practice. Despite early concerns regarding the safety of autologous fat into the breasts, recent studies have shown this to be both safe and effective. This study examines the use of autologous fat to replace and reconstruct the tissues removed in a left lower pole partial mastectomy for cancer in a patient treated with radiation. This represents a minimally-invasive, staged approach to the correction of a difficult problem.

Positive semidefinite tensor factorizations of the two-electron integral matrix for low-scaling ab initio electronic structure.

Tensor factorization of the 2-electron integral matrix is a well-known technique for reducing the computational scaling of ab initio electronic structure methods toward that of Hartree-Fock and density functional theories. The simplest factorization that maintains the positive semidefinite character of the 2-electron integral matrix is the Cholesky factorization. In this paper, we introduce a family of positive semidefinite factorizations that generalize the Cholesky factorization. Using an implementation of the factorization within the parametric 2-RDM method [D. A. Mazziotti, Phys. Rev. Lett. 101, 253002 (2008)], we study several inorganic molecules, alkane chains, and potential energy curves and find that this generalized factorization retains the accuracy and size extensivity of the Cholesky factorization, even in the presence of multi-reference correlation. The generalized family of positive semidefinite factorizations has potential applications to low-scaling ab initio electronic structure methods that treat electron correlation with a computational cost approaching that of the Hartree-Fock method or density functional theory.

Energies and structures in biradical chemistry from the parametric two-electron reduced-density matrix method: applications to the benzene and cyclobutadiene biradicals.

The treatment of biradical chemistry presents a challenge for electronic structure theory, especially single-reference methods, as it requires the description of varying degrees and kinds of electron correlation. In this work we assess the ability of the parametric two-electron reduced-density matrix (p2-RDM) method to describe biradical chemistry through application to the benzene and cyclobutadiene biradicals. The relative energy of o- and m-benzynes predicted by the p2-RDM method is consistent with Wenthold et al.'s experimental determinations, while the more difficult relative energy prediction of the more multi-referenced p-benzyne is within 1.4 kcal mol(-1) of the experimental value [P. G. Wenthold et al., J. Am. Chem. Soc., 1998, 120, 5279], which is significantly better than traditional single-reference methods. We observe that the degree of multireference correlation in the biradicals depends upon the distance between their radical centers, with the largest radical separation displaying the largest degree of multireference correlation. In addition to relative and absolute electronic energies, we report molecular geometries, natural orbitals, and natural-orbital occupations for the benzene and cyclobutadiene biradicals.

Finesse in forehead and brow rejuvenation: modern concepts, including endoscopic methods.

BACKGROUND: The brow and forehead are essential elements of the facial aesthetic architecture. Although frequently overlooked in youth, signs of facial aging are often most noticeable in the upper third of the face. Ptosis and loss of contour in the brows, along with temporal volume loss, sagging of periorbital tissue, and rhytides in the forehead, are common presenting complaints for aesthetic surgery. Although use of nonsurgical procedures (e.g., neuromodulators) has become very common practice, knowledge of surgical anatomy and interventions for brow and forehead rejuvenation are critical for a plastic surgeon. The earliest descriptions of brow-lift procedures are nearly a century old. Techniques have evolved significantly, to the point that patients may now return to work within 1 week of surgery, with minimal or no stigmata from an operation. METHODS: The literature and a series of cases from the senior surgeon (P.K.S.) were reviewed. RESULTS: A minimally invasive approach with an endoscope for dissection and repositioning of the brow was used in all patients. The authors have found that permanent suture fixation with cortical tunnels can produce an excellent, long-lasting aesthetic result for not only the forehead and brow but also the lateral periorbital and temporal regions. CONCLUSIONS: Although each operation is tailored to the patient's individual anatomy, the authors' approach to the endoscopic procedure is described in this article, along with a review of anatomical and surgical considerations. Finally, several patients provide demonstrative results from the senior surgeon's series of 546 patients.

Comparison of low-rank tensor expansions for the acceleration of quantum chemistry computations.

Low-rank spectral expansion and tensor hypercontraction are two promising techniques for reducing the size of the two-electron excitation tensor by factorizing it into products of smaller tensors. Both methods can potentially realize an O(r(4)) quantum chemistry method where r is the number of one-electron orbitals. We compare the two factorizations in this paper by applying them to the parametric 2-electron reduced density matrix method with the M functional [D. A. Mazziotti, Phys. Rev. Lett. 101, 253002 (2008)]. We study several inorganic molecules, alkane chains, and potential curves as well as reaction and dissociation energies. The low-rank spectral expansion, we find, is typically more efficient than tensor hypercontraction due to a faster convergence of the energy and a smaller constant prefactor in the energy optimization. Both factorizations are applicable to the acceleration of a wide range of wavefunction and reduced-density-matrix methods.

Relative energies and geometries of the cis- and trans-HO3 radicals from the parametric 2-electron density matrix method.

The parametric 2-electron reduced density matrix (2-RDM) method employing the M functional [Mazziotti, D. A. Phys. Rev. Lett. 2008, 101, 253002], also known as the 2-RDM(M) method, improves on the accuracy of coupled electron-pair theories including coupled cluster with single-double excitations at the computational cost of configuration interaction with single-double excitations. The cis- and trans-HO(3) isomers along with their isomerization transition state were examined using the recent extension of 2-RDM(M) to nonsinglet open-shell states [Schwerdtfeger, C. A.; Mazziotti, D. A. J. Chem. Phys. 2012, 137, 034107] and several coupled cluster methods. We report the calculated energies, geometries, natural-orbital occupation numbers, and reaction barriers for the HO(3) isomers. We find that the 2-RDM(M) method predicts that the trans isomer of HO(3) is lower in energy than the cis isomer by 1.71 kcal/mol in the correlation-consistent polarized valence quadruple-ζ (cc-pVQZ) basis set and 1.84 kcal/mol in the augmented correlation-consistent polarized valence quadruple-ζ (aug-cc-pVQZ) basis set. Results include the harmonic zero-point vibrational energies calculated in the correlation-consistent polarized valence double-ζ basis set. On the basis of the results of a geometry optimization in the augmented correlation consistent polarized valence triple-ζ basis set, the parametric 2-RDM(M) method predicts a central oxygen-oxygen bond of 1.6187 Å. We compare these energies and geometries to those predicted by three single-reference coupled cluster methods and experimental results and find that the inclusion of multireference correlation is important to describe properly the relative energies of the cis- and trans-HO(3) isomers and improve agreement with experimental geometries.

An anatomical evaluation and surgical approach to the perioral mound in facial rejuvenation.

BACKGROUND: Premature aging of the perioral soft tissues of the face is a common complaint of patients seeking facial rejuvenation, although its cause is unclear. The subcutaneous fat compartments of the face may be differentially affected by facial aging. Despite efforts to study and rejuvenate the aging periorbit, midface, and jowls, the effects of aging on the perioral mound have been less studied. METHODS: To better understand the cause of age-associated changes in the perioral area, a cadaver dissection study was performed. Eight fresh and fixed cadavers with evidence of perioral fullness were used in anatomical dissection. Anatomical observations and histologic examination were used to describe the age-related changes in this area. After describing the defect, the authors present a surgical approach to rejuvenation of this region, tailored to the findings in this anatomical study. RESULTS: Histologic sections demonstrated a lipomatous area without defined ligamentous attachments or encapsulations. Chambers of adipocytes in the hypodermis were separated by thin fibroseptations: a scaffold in the structural support of this region. Superficial lipodystrophy defines thisfacial region in the cadaver specimens. The end result is a fatty, ptotic perioral mound of tissue that is not well addressed by conventional rhytidectomy. CONCLUSIONS: The area of the perioral mound may represent a small, independent fat compartment or a differentially affected extension of the nasolabial compartment described by Pessa. This cadaver study has increased the authors' understanding of the perioral region and allowed them to improve results in its rejuvenation. The senior author's preferred approach is liposculpture with fine-cannula liposuction.

Skin flaps.

Open wounds, particularly around the face, often require complicated techniques for optimal closure. The approach to the closure of the complicated wound depends largely on the nature of the wound, including the location and size of the defect, the functional outcome after closure, the medical comorbidities of the patient, neighboring structures, and whether the defect is secondary to a malignancy or trauma. The goals of wound management are optimal aesthetic outcome, preservation of function, and patient satisfaction. The authors briefly review basic skin closure options and discuss use of skin flaps, particularly of the head and neck region.

Predictors of severity in deformational plagiocephaly.

Multiple risk factors for deformational plagiocephaly (DP) have been reported. The purpose of this study was to establish the impact of these variables on the severity of this deformity. A prospective cohort study was performed. Parents completed a standardized questionnaire assessing potential risk factors for DP before assessment. Examination included measurement of transcranial difference (TCD; ie, difference in oblique cranial lengths), evaluation of head tilt, and rotational asymmetry. Pearson correlation coefficient, 1-way analysis of variance, and 2-sample t-test were used to quantify the relationship between identified risk factors and TCD. A total of 434 patients with DP were evaluated. Male-to-female ratio was 2:1; mean gestational age was 36.5 weeks. Deformational plagiocephaly was first appreciated at a mean infant age of 6 weeks. A preexisting diagnosis of torticollis was noted in fewer than 50%. Mean TCD was 11.2 mm. Head tilt was documented in 80% of infants, and mean head rotational asymmetry was 16.4 degrees. Deformational plagiocephaly was more severe in multiple birth pregnancies (P < 0.05), males (P < 0.05), infants with a favorite head position (P < 0.01), preexamination diagnosis of torticollis (P < 0.05), and infants with a head tilt (P < 0.05). Lower gestational age (P < 0.05) and greater head rotational asymmetry (P < 0.0001) were found to correlate with DP severity. This study suggests that the relationship between the severity of DP and certain risk factors can be quantified. The presence and degree of cervical imbalance correlate strongly with deformational cranial asymmetry.

Reconstruction of musculoskeletal defects following oncologic resection in 76 patients.

Between 1990 and 2002, 76 patients underwent 102 muscle flap reconstructions for extremity sarcomas. The patients had radical resection with immediate reconstruction. Reconstructions were performed by the Musculoskeletal Oncology and Plastic Surgery services. The mean age of our patients was 39.1 years. Patients were studied for a mean of 25.4 months. There were 79 pedicle flaps and 23 free flaps. Complications occurred in 23.7% of patients, including wound necroses, seromas, postoperative bleeding, postoperative infections, and flap loss. Five patients required a secondary flap procedure. The overall flap survival rate was 98%. Three patients had local recurrences. Sixteen patients (21.1%) have died of their disease. Five patients are alive with metastases. In 54 patients, Musculoskeletal Tumor Society (MSTS) functional evaluation scores averaged 27.1 (range, 12-30). In this large series of patients, we have demonstrated that, although minor complications are common, functional limbs can be salvaged following oncologic resection from the extremities.

Skin flaps.

Open wounds, particularly around the face, often require complicated techniques for optimal closure. The approach to the closure of the complicated wound depends largely on the nature of the wound, including the location and size of the defect, the functional outcome after closure, the medical comorbidities of the patient, neighboring structures, and whether the defect is secondary to a malignancy or trauma. The goals of wound management are optimal aesthetic outcome, preservation of function, and patient satisfaction. The authors briefly review basic skin closure options and discuss use of skin flaps, particularly of the head and neck region.

The female intestine is more resistant than the male intestine to gut injury and inflammation when subjected to conditions associated with shock states.

Having documented that proestrus female rats are more resistant to shock-induced acute gut and hence lung injury than male rats, we tested the hypothesis that the female gut is more resistant to injury and produces less of an inflammatory response than the male gut when exposed to conditions associated with shock states (hypoxia and acidosis) utilizing the ex vivo Ussing chamber system. Ileal mucosal membranes harvested from normal male and female rats mounted in Ussing chamber systems were exposed to normoxia or 40 min of hypoxia at a normal pH (pH 7.3) or acidosis (pH 6.8). Cytokine and nitric oxide levels in the serosal compartment of the Ussing chamber were measured at the end of the 3-h experimental period to assess the immunoinflammatory response, whereas FITC-dextran (mol wt 4,300) was employed to assess barrier function. Histomorphological changes were used to quantitate gut mucosal injury. Hypoxia, acidosis, or hypoxia plus acidosis was associated with a significant increase in proinflammatory cytokine production [interleukin (IL)-6, tumor necrosis factor, and macrophage inflammatory protein (MIP)-2] by the male compared with the female intestinal segments. In contrast, the female gut manifested a higher anti-inflammatory response (nitric oxide and IL-10) and improved intestinal barrier function as well as less evidence of mucosal injury than the male intestinal segments. Administration of estradiol or the testosterone receptor antagonist, flutamide, to male rats abrogated the increase in gut injury and the increased IL-6 and MIP-2 response observed after hypoxia plus acidosis. These results suggest that gender differences in the ex vivo intestinal response to stresses, such as hypoxia and acidosis, exist and that the administration of estradiol or blockade of the testosterone receptor to male rats mitigates these gender differences.