Environment region

Another major externality that will shape the electricity sector is the environmental impact of energy use at all geographical scales - smog and particulates in urban environments, regional acid rain, global warming. 

Figure A2.1.1 A representation of a vapor-pressure-evaluating system. Region A includes the sample and its environment. Region B is a vapor transfer path to the sensor region, C, which includes the sensor and its environment. TA and Tc are the temperatures in regions A and C, respectively.

Garrett, C.L. and Shrimpton, J.A. (1997) Organotin Compounds in the British Columbia Environment, Regional Program Report No. 98-03, Environment Canada, Environmental Protection Service, Pacific and Yukon Region, Vancouver, BC, Canada. 

The cell interior, Region i (S < 0), interacts with the environment, Region e (S > 0), via the membrane (S = 0). The same notation is also used for the case where the above object represents a cell mass. 

The dQJdt term is the air flow rate and the dQ f//dt term the water flow velocity. These terms would have units of m s The k terms are degradation first order values (dc/dt = -kc) [3] specific to each environment region. The differential equation can be simplified as ... 

AU the QM/MM methods dedicated to treat solution chemistry are based on the definition of two zones (i) an active region that is generally defined as a sphere around the reactive center and (ii) an environment region that embeds the active region. This is illustrated in Fig. 2.1. The active region generally includes the reactive center (the orange disk in Fig. 2.1) and at least the first coordination sphere and is described at the QM level. QM molecules will always be shown in... 

Ball Stick in the Figures. The environment region includes the bulk solvent molecules described at the MM level, and will be depicted with lines. Each solvent molecule is either in the active zone, or in the transition region or in the environment zone. The QM/MM border does not cut through solvent bonds, even though methods that allow it have been developed [29]. 

As mentioned in the introduction, there are two main classes of methods. The first class constrains the QM molecules to remain inside the active region, while simultaneously keeping the MM molecules in the environment region (outside the active region). The solvent molecules cannot diffuse across the boundary between the active region and the environment. The most prominent examples of this approach will be discussed in Sect. 2.2.1. The second class of methods discussed does allow the solvent molecules to diffuse across the QM/MM boundary, changing the nature (QM vs. MM) of those molecules on the fly. This change can be instantaneous [16, 30-32] (Sect. 2.2.2 Discontinuous adaptive QM/MM), or smooth [33-35] (Sect. 2.2.3 Continuous adaptive QM/MM). 

This separation is exact, and implementing the integral of Eq. (2.4) into Eq. (2.2) has the factors C cancel in the numerator and denominator, yielding an unchanged thermodynamic average (x), provided that the molecules in the active and environment region do not interchange [41]. 

For a system with M solvent molecules in the transition region, the maximum number of partitions that can meaningfully contribute to this partial character corresponds to the 2 possible partitions of the M molecules into two sets. The behavior of the weight functions (r) is such that when a solvent molecule m, moves away from the QM center, the weight (r) of a partition n that describes rrii QM decreases, becoming zero as m exits the transition region and enters the environment region. 

The QM and MM descriptions were selected based on two requirements (1) The MM force field should allow proton shuttling in the environment region, and... 

We started the QM/MM simulations with the hydroxide far away from Omc, at approximately 10 A, which is well inside the environment region. The hydroxide ion is therefore initially described MM. At the start of all five QM/MM simulations, we observed fast consecutive proton transfer occurrences at the start of the simulations, involving the hydroxide ion and neighboring water molecules. An initial fast and frequent shuttling of the proton back and forth between two oxygen atoms is then suddenly followed by a large displacement of the QH ion, always in the direction of the central methanol molecule. Fig. 2.16c displays the distance between the OH ion and the methanol Omc atom, which suddenly decreases within the first 2.5 ps of the simulation. The OH ion then finds itself inside the active region boundary, where it stays for the remainder of the simulation. 

We propose a grid based model homogeneous or not composed with a set of codes representing blocs of elementary cells. The used code is such it defines the size of an environment region, the links with the other codes and its grid location. 

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