[DFTB-Plus-User] Help on melting quartz to obtain amorphous silica

[Ben Hourahine]

Hello,

melting tends to proceed from defects, so its quite possible that your 
annealing never left the free energy
minima of the perfect crystal (just ending up super-heating the 
crystobalite structure above its melting
point and then cooling down again). Did you look at the structure at 
high temperatures?

Regards

Ben

On 22/05/13 02:51, 苏锐 wrote:
> Hi!
>     I am now trying to obtain amorphous silica through the melting and 
> quenching procedure. The initial system is built using a 2x2x2 
> supercell of beta-cristobalit containing 192 atoms. I meet a problem 
> that the quenched structure is “defect free”. That means no 
> non-bridging oxygen atoms or 5-member rings etc. that might exist in 
> amrphous structure. I think there might be some error in my md input. 
> Would someone have a look at my input and give some advices?
>    Here is my input:
> Geometry = GenFormat {
>     <<< silica222.gen
> }
> Driver = VelocityVerlet {
>     MovedAtoms    = 1:-1
>     TimeStep [fs] = 1.0
>     Thermostat = NoseHoover {
>         Temperature [Kelvin] = TemperatureProfile {
>             # initial temperature = 4000K
>             constant    1    4000
>             # melt at 4000K for 5ps = 5000 step
>             constant    5000 4000
>             # reduce to 3000 in 20ps
>             exponential 20000 300
>             # equilibrium at 300K
>             constant    5000 300
>         }
>         CouplingStrength [cm^-1] = 3000
>     }
>     MDRestartFrequency = 100
>     OutputPrefix       = "amorphous_md"
> }
> Hamiltonian = DFTB {
>     SCC = Yes
>     SlaterKosterFiles = {
>         Si-O  = "./skf/Si-O.skf"
>         O-Si  = "./skf/O-Si.skf"
>         Si-Si = "./skf/Si-Si.skf"
>         O-O   = "./skf/O-O.skf"
>     }
>     MaxAngularMomentum = {
>         O  = "p"
>         Si = "d"
>     }
>     Filling = Fermi {
>         Temperature [Kelvin] = 300.0
>     }
>     KPointsAndWeights = {
>         0.0 0.0 0.0 1.0
>     }
> }
> Options {}
> ParserOptions {
>     ParserVersion = 4
> }

-- 
       Dr. B. Hourahine, SUPA, Department of Physics,
     University of Strathclyde, John Anderson Building,
             107 Rottenrow, Glasgow G4 0NG, UK.
     +44 141 548 2325, benjamin.hourahine at strath.ac.uk

   Strathclyde 2012 THE Awards UK University of the Year

    The University of Strathclyde is a charitable body,
         registered in Scotland, number SC015263

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