Predicting the conductance of strongly correlated molecules: the Kondo effect in perchlorotriphenylmethyl/Au junctions.

Stable organic radicals integrated into molecular junctions represent a practical realization of the single-orbital Anderson impurity model. Motivated by recent experiments for perchlorotriphenylmethyl (PTM) molecules contacted to gold electrodes, we develop a method that combines density functional theory (DFT), quantum transport theory, numerical renormalization group (NRG) calculations and renormalized super-perturbation theory (rSPT) to compute both equilibrium and non-equilibrium properties of strongly correlated nanoscale systems at low temperatures effectively from first principles. We determine the possible atomic structures of the interfaces between the molecule and the electrodes, which allow us to estimate the Kondo temperature and the characteristic transport properties, which compare well with experiments. By using the non-equilibrium rSPT results we assess the range of validity of equilibrium DFT + NRG-based transmission calculations for the evaluation of the finite voltage conductance. The results demonstrate that our method can provide qualitative insights into the properties of molecular junctions when the molecule-metal contacts are amorphous or generally ill-defined, and that it can further give a fully quantitative description when the experimental contact structures are well characterized.

Assessment of density functional theory for iron(II) molecules across the spin-crossover transition.

Octahedral Fe(2+) molecules are particularly interesting as they often exhibit a spin-crossover transition. In spite of the many efforts aimed at assessing the performances of density functional theory for such systems, an exchange-correlation functional able to account accurately for the energetic of the various possible spin-states has not been identified yet. Here, we critically discuss the issues related to the theoretical description of this class of molecules from first principles. In particular, we present a comparison between different density functionals for four ions, namely, [Fe(H(2)O)(6)](2+), [Fe(NH(3))(6)](2+), [Fe(NCH)(6)](2+), and [Fe(CO)(6)](2+). These are characterized by different ligand-field splittings and ground state spin multiplicities. Since no experimental data are available for the gas phase, the density functional theory results are benchmarked against those obtained with diffusion Monte Carlo, one of the most accurate methods available to compute ground state total energies of quantum systems. On the one hand, we show that most of the functionals considered provide a good description of the geometry and of the shape of the potential energy surfaces. On the other hand, the same functionals fail badly in predicting the energy differences between the various spin states. In the case of [Fe(H(2)O)(6)](2+), [Fe(NH(3))(6)](2+), [Fe(NCH)(6)](2+), this failure is related to the drastic underestimation of the exchange energy. Therefore, quite accurate results can be achieved with hybrid functionals including about 50% of Hartree-Fock exchange. In contrast, in the case of [Fe(CO)(6)](2+), the failure is likely to be caused by the multiconfigurational character of the ground state wave-function and no suitable exchange and correlation functional has been identified.

Electric field control of valence tautomeric interconversion in cobalt dioxolene.

We demonstrate that the critical temperature for valence tautomeric interconversion in cobalt dioxolene complexes can be significantly changed when a static electric field is applied to the molecule. This is achieved by effectively manipulating the redox potential of the metallic acceptor forming the molecule. Importantly, our accurate density functional theory calculations demonstrate that already a field of 0.1 V/nm, achievable in Stark spectroscopy experiments, can produce a change in the critical temperature for the interconversion of 20 K. Our results indicate a new way for switching on and off the magnetism in a magnetic molecule. This offers the unique chance of controlling magnetism at the atomic scale by electrical means.

The role of silicone stents in the treatment of cicatricial tracheal stenoses.

OBJECTIVE: Tracheal stenting for cicatricial stenoses is reserved for patients whose lesions are deemed inoperable for local or general reasons. The aim of our study was to verify the long-term results of silicone tracheal stents in such a clinical setting. METHODS: Clinical data of 45 patients treated by tracheal silicone stents, between 1987 and 1999, were reviewed. All patients had highly symptomatic cicatricial stenoses; they were selected for stenting rather than for surgery because of local and general conditions. This series has been divided in two groups according to the purpose of stenting: bridge to surgery or definitive treatment. Follow-up ranged between 12 and 83 months. Twenty-seven patients received a Montgomery T tube (Hood Laboratories, Pembroke, Mass), 16 a Dumon stent (Novatech, Plan de Gras, France), and 2 a Dynamic stent (Rusch, Kernen, Germany). RESULTS: No procedure-related mortality was observed. Nine patients underwent curative resection and reconstruction after a variable stenting period; one had a recurrent stenosis and was treated for palliation with a T tube. Tracheal stenting was performed for palliation as a definitive treatment in 37 patients. Among this group, 11 patients died of unrelated causes at a median of 10 months after the endoscopic treatment. The stent was permanently removed in 10 after a median interval of 32 months (range 9-70 months); in 4 others, symptomatic recurrence of the stenosis was observed within 6 weeks of stent removal. None of the patients successfully decannulated had a completely normal tracheal lumen but all remained asymptomatic because the residual stenosis was mild or well tolerated for concomitant limitation of physical activity. CONCLUSIONS: Long-term treatment with a silicone stent was safe and well tolerated in cicatricial tracheal stenoses. This procedure can be considered as a bridge to curative surgery or as a definitive treatment. The latter, generally performed for palliation, may provide satisfactory therapeutic results in selected patients, even in the presence of severe circumferential stenoses.

[Surgical treatment of thyroid cancer in 243 cases]. / Trattamento chirurgico del cancro della tiroide in 243 casi.

The incidence of thyroid cancer, which accounts for 1-2% of all malignancies, constantly increasing. Its management requires an integrated approach, in which the surgeon plays a pivotal role, providing the basis for further treatment. At present, the extent of exeresis, the lymph-node dissection technique and the management of upper respiratory-digestive tract infiltration are still debatable issues. The authors report on their experience with 243 surgically treated thyroid malignancies over the period from January 1986 to December 1999. The operations performed were: total thyroidectomy 226 cases, lobo-isthmectomy 3 cases, total thyroidectomy + lung metastasectomy 1 case, total thyroidectomy + SE quadrantectomy 1 case, total thyroidectomy + monolateral modified neck dissection 30 cases, total thyroidectomy + bilateral modified neck dissection 17 cases, total thyroidectomy + radical neck dissection 1 case, total thyroidectomy + tracheal sleeve resection 5 cases. In 9 cases, extensive tracheal involvement (5.5 cm), age or neoplastic histology allowed only palliative treatment (endoscopic recanalization + tracheal endoprosthesis or tracheostomy. Nd-Yag laser endoscopic recanalization was performed in 2 patients as a preliminary stage in subsegmental radical treatment, and in 5 cases for palliation. Recurrent laryngeal nerve palsy occurred in 3 cases, long-term hoarseness in 2, and hypoparathyroidism in 4. The overall mean hospital stay was 4.8 days. Of 299 patients still alive, 215 are free of disease. Surgery is the treatment of choice, with the goal of completely removing the neoplasm, together with any anatomical structures involved in infiltration (muscles, respiratory-digestive tract, lymph nodes). Satisfactory palliation can be achieved by endoprosthesis deployment or tracheostomy in all cases where surgery is ruled out due to extent of disease, patient age or histological type.

[Conservative surgery in the treatment of rectal tumors. Our experience, 1986-1997]. / La chirurgia conservativa nel trattamento dei tumori del retto. Nostra esperienza 1986-1997.

OBJECTIVE: Our institution's experience with low anterior resection for primary rectal cancer was reviewed to determine cancer treatment results and to identify risk factors for pelvic recurrence. METHODS: Ninety-two patients treated for primary rectal cancer between 1986 and 1997 were studied retrospectively. All cases was classified according to Astler-Coller. Median follow up was 46 months. RESULTS: Actuarial 5-year survival for all patients was 79%. Among 28 patients who relapsed, only 9 pelvic recurrence was detected with an actuarial rate of 15% at 5 years. Lymph nodes involvement were associated with increased risk for pelvic recurrence. DISCUSSION: Low anterior resection permitted by circular stapler provides good treatment for mid-rectal cancers and for some distal rectal cancers. Pelvic recurrence is not correlated with neoplasm localization, T stage and short distal resection margins, but only with the presence of lymph nodes involvement. This result increase the value of the hypothesis that search the pelvic recurrence origin in a extra-parietal disease respect anastomotic disease. CONCLUSION: Fundamental to prevent pelvic recurrence is the surgical technique that have to remove lymph node en bloc with the rectum doing a dissection along the endopelvic fascia to Denonvillers fascia so to take away completely the mesorectum.