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

[苏锐]

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
}
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