Crystalline condensed phase calculations

It is relevant in this context that, in work on the cleavage force of crystalline Si, Matthai and March [49] have used a coordination-dependent force field due to Tersoff [50] to study related bond-breaking1 in a condensed phase. Tersoff s force field was fitted to available density-functional calculations, With such a force law, Matthai and March [49] concluded that the Si bond is comparable in... 

As an example, the heat of combustion of 1,3-cyclohexanedione was foimd to be -735.9 kcal/mol. ° Taking -94.05 kcal/mol and —68.32 kcal/mol as the standard heats of formation of CO2 and H2O, respectively, gives a standard heat of formation for crystalline 1,3-cyclohexanedione of 6(—94.05) -I- 4 (-68.32) - (-735.9) = -101.68 kcal/mol. It is sometimes necessary to correct heats of reaction for the heats associated with phase changes in the reactants or products. To convert from a condensed phase to the gas phase (e.g., for comparison with values calculated theoretically) the relevant terms are the heat of vaporization (Af/°) of a liquid or heat of sublimation (AW°) of a solid." " Correcting for the standard heat of sublimation of l -cyclohex-anedione, +21.46 kcal/mol, gives its standard heat of formation in the gas phase of -80.22 kcal/mol. 

In calculating the distribution of rare-earth elements, or indeed any other trace elements, between a gas of solar composition and condensing crystalline phases there are two basic steps. Firstly, the distribution of rare-earth species in the nebula must be estimated and secondly, the partition of the REE between the gas and solid phases calculated. In the ensuing discussion it is ass amed following Grossman (197 ) and Boynton (1975), that equilibrium was achieved in the condensing solar nebula. 

A number of other thermodynamic properties of adamantane and diamantane in different phases are reported by Kabo et al. [5]. They include (1) standard molar thermodynamic functions for adamantane in the ideal gas state as calculated by statistical thermodynamics methods and (2) temperature dependence of the heat capacities of adamantane in the condensed state between 340 and 600 K as measured by a scanning calorimeter and reported here in Fig. 8. According to this figure, liquid adamantane converts to a solid plastic with simple cubic crystal structure upon freezing. After further cooling it moves into another solid state, an fee crystalline phase. 

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