[DFTB-Plus-User] simulation of a water box with periodic boundary conditions

[mjyang]

Dear Benjamin,
  
Thanks for your reply. 
What will be the propriate KPointsAndWeights values for a protein solvated into a water box?
I am not very clear about the relation between the delocalization of MOs in the system and the values of KPointsAndWeights set.

Many thanks.

Mingjun
________________________________________
From: dftb-plus-user-bounces at dftb-plus.info [dftb-plus-user-bounces at dftb-plus.info] On Behalf Of Benjamin Hourahine [benjamin.hourahine at strath.ac.uk]
Sent: Monday, March 26, 2012 5:15 AM
To: User list for DFTB+ related questions
Subject: Re: [DFTB-Plus-User] simulation of a water box with periodic boundary  conditions

Dear Mingjun,

1) it is only the length of the box sides (and their angles) which matter, so your example is correct.

2) Water has strongly localised molecular orbitals, so the gamma point is probably sufficient for
a periodic calculation (as always with numerical parameters, you should test the convergence of the
property you want to calculate with respect to increasing the grid):

KPointsAndWeights = { 0.0 0.0 0.0 1.0}

Depending on what you are calculating, you may also need to use dispersion, 3rd order and damping.

________________________________________
From: dftb-plus-user-bounces at dftb-plus.info [dftb-plus-user-bounces at dftb-plus.info] On Behalf Of mjyang [mjyang at hku.hk]
Sent: 25 March 2012 11:30
To: dftb-plus-user at dftb-plus.info
Subject: [DFTB-Plus-User] simulation of a water box with periodic boundary      conditions

Dear all,

    I am going to simulate a water box under periodic conditions and have some questions:
1. can I set the LatticeVectors as follows if the box size is 45.1049*42.5232*45.5762:
 LatticeVectors [Angstrom] = {
        45.1049 0. 0.
        0. 42.5232 0.
        0. 0. 45.5762
    }

Or I should set it by the exact value of the minimum and maximum coorinates the box occupied along x, y, z axis?

2. If I am only interested in the converged energy and charges of the system, how should I set the Hamiltonian, especially the keywords KPointsAndWeights?

Many thanks.


Mingjun Yang

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