Computation of charge distribution and electrostatic potential in silicates with the use of chemical potential equalization models

New parameters for the electronegativity equalization model (EEM) and the split-charge equilibration (SQE) model are calibrated for silicate materials, based on an extensive training set of representative isolated systems. In total, four calibrations are carried out, two for each model, either using iterative Hirshfeld (HI) charges or ESP grid data computed with density functional theory (DFT) as a reference. Both the static (ground state) reference quantities and their responses to uniform electric fields are included in the fitting procedure. The EEM model fails to describe the response data, whereas the SQE model quantitatively reproduces all of the training data. For the ESP-based parameters, we found that the reference ESP data are only useful at those grid points where the electron density is lower than 0.001 a.u. The density value correlates with a distance criterion used for selecting grid points in common ESP fitting schemes. All parameters are validated with DFT computations on an independent set of isolated systems (similar to the training set), and on a set of periodic systems including dense and microporous crystalline silica structures, zirconia, and zirconium silicate. Although the transferability of the parameters to new isolated systems poses no difficulties, the atomic hardness parameters in the HI-based models must be corrected to obtain accurate results for periodic systems. The SQE/ESP model permits the calculation of the ESP with similar accuracy in both isolated and periodic systems

Environmental conditions of interstadial (MIS 3) and features of the last glacial maximum on the King George island (West Antarctica)

The interstadial marine deposits stratum was described in the Fildes Peninsula (King George Island) due to field and laboratory investigations during 2008–2011. The stratum fragments occur in the west and north-west parts of peninsula in following forms: sections of soft sediments, containing fossil shells, marine algae, bones of marine animals and rich marine diatom complexes in situ (11 sites); fragments of shells and bones on the surface (25 sites). According to the results of radiocarbon dating, these deposits were accumulated within the period 19–50 ky BP. Geographical and altitude settings of the sites, age characteristics, taxonomy of fossil flora and fauna, and good safety of the soft deposits stratum allow to make following conclusions: during interstadial, sea water covered significant part of King George Island up to the present altitude of 40 m a.s.l., and the King George Island glaciation had smaller size then; environmental conditions for the interstadial deposit stratum accumulation were at least not colder than today; probably, the King George island territory was covered entirely by ice masses of Last glacial maximum not earlier than 19 ky BP; during Last glacial maximum, King George Island was covered by thin, «cold», not mobile glaciers, which contribute to conservation of the soft marine interstadial deposits filled with fossil flora and fauna

Условия интерстадиала (MIS3) и характер оледенения в последний ледниковый максимум на о. Кинг Джордж (Западная Антарктика)

The interstadial marine deposits stratum was described in the Fildes Peninsula (King George Island) due to field and laboratory investigations during 2008–2011. The stratum fragments occur in the west and north-west parts of peninsula in following forms: sections of soft sediments, containing fossil shells, marine algae, bones of marine animals and rich marine diatom complexes in situ (11 sites); fragments of shells and bones on the surface (25 sites). According to the results of radiocarbon dating, these deposits were accumulated within the period 19–50 ky BP. Geographical and altitude settings of the sites, age characteristics, taxonomy of fossil flora and fauna, and good safety of the soft deposits stratum allow to make following conclusions: during interstadial, sea water covered significant part of King George Island up to the present altitude of 40 m a.s.l., and the King George Island glaciation had smaller size then; environmental conditions for the interstadial deposit stratum accumulation were at least not colder than today; probably, the King George island territory was covered entirely by ice masses of Last glacial maximum not earlier than 19 ky BP; during Last glacial maximum, King George Island was covered by thin, «cold», not mobile glaciers, which contribute to conservation of the soft marine interstadial deposits filled with fossil flora and fauna.В ходе экспедиционных и лабораторных работ 2008–2012 гг. изучены распространённые на п-ове Файлдс (о. Кинг Джордж) морские отложения интерстадиала. Разрезы отложений в ненарушенном залегании, содержащие морские комплексы диатомей, раковины, водоросли и кости морских животных, исследованы в 11 точках; высыпки раковин и костей на поверхности мысов, морен и склонов долин установлены в 25 точках. Согласно радиоуглеродному датированию, эти отложения накапливались в период между 19 и 50 тыс. л.н. Пространственное и высотное положение отложений, их строение, возраст, а также особенности видового состава ископаемой флоры и фауны позволяют заключить следующее: 1) в период интерстадиала морские воды распространялись на о. Кинг Джордж как минимум до современных высотных отметок 40 м, а площадь острова и оледенения заметно сокращалась; 2) условия накопления отложений интерстадиала были, по крайней мере, не холоднее наблюдающихся в этом районе сейчас; 3) развитие оледенения последнего ледникового максимума (ПЛМ) на о. Кинг Джордж началось довольно поздно; возможно, до 19 тыс. л.н. остров не был полностью покрыт льдом; 4) оледенение ПЛМ на о. Кинг Джордж было маломощным, малоподвижным («холодного» типа) и, вероятно, было представлено несколькими ледниками с низкими потенциалом экзарации и способностью «консервировать» древние отложения