NWChem: Past, present, and future.

Specialized computational chemistry packages have permanently reshaped the landscape of chemical and materials science by providing tools to support and guide experimental efforts and for the prediction of atomistic and electronic properties. In this regard, electronic structure packages have played a special role by using first-principle-driven methodologies to model complex chemical and materials processes. Over the past few decades, the rapid development of computing technologies and the tremendous increase in computational power have offered a unique chance to study complex transformations using sophisticated and predictive many-body techniques that describe correlated behavior of electrons in molecular and condensed phase systems at different levels of theory. In enabling these simulations, novel parallel algorithms have been able to take advantage of computational resources to address the polynomial scaling of electronic structure methods. In this paper, we briefly review the NWChem computational chemistry suite, including its history, design principles, parallel tools, current capabilities, outreach, and outlook.

Application of high-level iterative coupled-cluster methods to the cytosine molecule.

The need for inclusion higher-order correlation effects for adequate description of the excitation energies of the DNA bases became clear in the past few years. In particular, we demonstrated that the inclusion of triply excited configurations may play an important role in a proper description of the excitation energies of the cytosine molecule in realistic environment. In this paper we discuss the accuracies of excitation energies for the cystosine molecule in the gas phase and in the aqueous solution calculated with noniterative and iterative coupled-cluster methods that include the effect of triply excited configurations.

[Functional state of the resected stomach stump in peptic ulcer]. / Funktsional'noe sostoianie kul'ti rezetsirovannogo zheludka u bol'nykh iazvennoi bolezn'iu

The authors report the results of examination of 80 patients with ulcerous disease of the stomach and duodenum prior to and in the immediate period, as well as in 85 patients in late terms after typical Hofmeister-Finsterer gastrectomy. The acid-production of the stomach and its stump was studied by intragastric pH-metry, pepsine in the gastric juice was determined and also the resected stomach excretory function was studied by fibrochromogastroscopy. It is shown that the method of intragastric pH-metry is more advanrageous, since it gives an estimation of acid-production of the resected stomach in the immediate postoperative period, in particular.

[A comparative evaluation of the results of traditional and laser stomach resection]. / Sravnitel'naia otsenka rezul'tatov traditsionnoi i lazernoi rezektsii zheludka.

Comparative evaluation of immediate and long-term results of gastric resection was made in 89 patients operated upon by a traditional method and in 69 patients after laser operations. It was found that laser scalpel used in gastric resection gives reliable hemostasis, reduces the intraoperative blood loss and the time of creation of gastroenteric anastomosis. At the same time 2 times greater amount of inflammatory complications of the anastomosis was noted. The cause of the development of anastomosis after laser resection of the stomach is discussed.

Calculations of molecular properties in hybrid coupled-cluster and molecular mechanics approach.

We report benchmark calculations obtained with our new coupled-cluster singles and doubles (CCSD) code for calculating the first- and second-order molecular properties. This code can be easily incorporated into combined [Valiev, M.; Kowalski, K. J. Chem. Phys. 2006, 125, 211101] classical molecular mechanics (MM) and ab initio coupled-cluster (CC) calculations using NWChem, enabling us to study molecular properties in a realistic environment. To test this methodology, we discuss the results of calculations of dipole moments and static polarizabilities for the Cl2O system in the CCl4 solution using the CCSD (CC with singles and doubles) linear response approach. We also discuss the application of the asymptotic extrapolation scheme (AES) [Kowalski, K.; Valiev, M. J. Phys. Chem. A 2006, 110, 13106] in reducing the numerical cost of CCSD calculations.