fsn_ 857-veryazov an-2.hydratio

1、AtomisticmodellingofcrystalstructureofCSHwithhighCSratioGanKova?evi?1LucNicoleau2rNonat3ValeraVeryazov41.DivisionofMaterialPhysicsRu?erBo?kovi?InstituteZagreb10002Croatia2.BASFConstructionSolutionsGmbHGMBMTrostberg83304G

2、ermany3.LabatoireInterdisciplinaireCarnotdeBourgogneUniversitdeBourgogneDijon47870France4.DivisionofTheeticalChemistryLundUniversityLund22100SwedenAbstractTheatomicstructureofcalciumsilicatehydrate(C1.67SHx)hasbeenstudie

3、d.AtomisticCSHmodelssuggestedinourpreviousstudyhavebeenrevisedindertoperfmadirectcomparisonofenergeticstabilityofthedifferentstructures.AnextensivesetofperiodicstructuresofCSHwithvariationofwatercontentwascreatedthenopti

4、mizedusingmoleculardynamicswithreactivefcefieldReaxFFquantumchemicalsemiempiricalmethodPM6.ThenewgeometriesofCSHreptedinthispapershowlowerrelativeenergywithrespecttothegeometriesfromtheiginaldefinitionofCSHmodels.Modelth

5、atcrespondstocalciumenrichedtobermitestructurehasthelowestrelativeenergythedensityclosesttotheexperimentalvalues.iginalityThedetailedatomisticdeionofCSHisessentialfunderstingchemistryofcementconcrete.Inthecurrentstudywes

6、uggestednewstructuresfCSHwithhighCSratio.Theverificationofthestructureswasperfmedbymoleculardynamicssimulationsquantumchemicalcalculations.Theobtainedperiodicstructurescanbeusedinfuturetheeticalinvestigationsofthestabili

7、tyofrealsizeparticlesofCSH.Keywds:CSHstructureatomisticsimulationReaxFFfcefieldsemiempiricalquantumchemistry1Therefeinthecurrentstudywehavemodifiedthealgithmsusedin(Kova?evi?G.etal.2015)appliedadditionalconditionsoallstr

8、uctureshaveanidenticalchemicalcompositionperunitcell(bothinsideonemodelacrossdifferentmodels).ThischangeofalgithmsredefinedmodelsfCSHlabels1a2a3awillbeusedfthegroupsofcodinateswhichbelongtotheseredefinedmodels.Theatomicc

9、ompositionofanunitcellofeachstructureisidenticalthusthetotalenergiescanbecompareddirectlywithoutanyadditionalapproximationsassumptions.2.Theconstructionofgeometricalmodels2.1.CrystallographicmodelsofCSHThegeometriesbelon

10、gingtomodels1a–3aareconstructedfromthesameinitialstructureoftobermite11suggestedat(MerlinoS.etal.2001).Redefinedmodel1aiscreatedfollowingthesamewayasmodel1:byfragmentinginfinitesilicachainsoftobermitebyromlyremovingsilic

11、amonomersfromSi2sites(generallyreferredtobridgingtetrahedrons)adjustingtheexpectedCSratio(1.67)byaddingCaatomsintotheinterlayer.Sincemodel1had17%meatomsthanmodels23model1aiscreatedsmallerthanmodel1indertohavethesamenumbe

12、rofatomsasmodels2a3a.Initialunitcellsofmodels1awerecreatedasa341supercelloftobermite11(seeTable1)Table1:Unitcellsizesofmodels1a2a3a.Unitcellsarenotoptimized.αγanglesare90.0deg.model1amodel2amodel3aa29.4836.8436.84b20.951

13、9.9019.90c22.7822.6822.68βdeg58.1758.1758.17Model2awascreatedthesamebasicideaasfmodel2:removingfourconsecutivesilicaatomsfromtheinfinitesilicachainsoftobermite.ThesefourconsecutivesilicaatomsarealwaysSi2Si1Si3Si2position

14、sthepositionofthechainisedromlyindertocreatethedistributionofsilicadimerspentamers.22calciumatomshavetoberemovedfromthestructureindertomakethecrectCSratiotomakethestructureswiththesamenumberofatomsasinstructuresofmodel1a

15、.Unitcellsofmodel2aare351supercellsoftobermite.Unlikemodel2wheresilicaunitswereheavilyprotonatedinmodel2asilicaunitswereleftwithouthydrogenatoms.Model3awascreatedinasimilarfashionasmodel3:withromremovalofsiliconatomsnoma

16、tteronthesiteoftheremovedatom.TheratioofsilicaunitsinQ1Q2sitesinoligomerscreatedbyromremovalofsilicaunitsfrominfinitesilicachainsdoesnotmatchexperimentallyobservedQ1Q2ratio.Alsoromremovalofsilicaunitsproducesabout36%sili

17、camonomerswhichisbyfargreaterthanexperimentallyobservedamountinsamplesthatarepossiblycontaminatedwiththeC3Sphase.Therefewediscardedallstructureswithlessthan12%ofSi(Q0)atomsmethan86%Si(Q1)atomsmethan14%Si(Q2)atoms.Thismak