Quasiatomic Orbitals (QO)
&mdash Ab Initio Tight-Binding Method

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Please cite our paper if you use subroutines in this package. Thanks.

Xiaofeng Qian, Ju Li, Liang Qi, Cai-Zhuang Wang,
Tzu-Liang Chan, Yong-Xin Yao, Kai-Ming Ho, and Sidney Yip,
"Quasiatomic orbitals for ab initio tight-binding analysis",
Phys. Rev. B 78 (2008) 245112

[---Source code of our new QO method will be released soon. (QO Data Archive) ---]
[---Source code of the original QUAMBO method is released.---]




Input file example:
Output files list:


Current version for QO method: not available yet.
Current version for QUAMBO method (last update at 5/23/2007):
QUAMBO_version_1.1 for both VASP and DACAPO.

Note that the source code of the QUAMBO method is NOT the same as that developed by Lu and Wang at AMES lab (the latter one has not been released yet). It is a totally different implementation, especially our code can deal with NCPP/USPP/PAW method in Dacapo or VASP packages.






FAQ for the original QUAMBO method

[FAQ for our new QO method will be updated soon.]

  1. Why is the condition number very bad(large) sometimes?

    This question is related to several possible reasons:

    (a) insufficient number of bands in your DFT calculation
    Normally beside N_occ occupied bands(ie. N_occ=10), you need to include N_unocc unoccupied bands to grab unoccupied antibonding states. To be safe, you can choose N_unocc = N_occ(ie. N_unocc=10), therefore N_total_bands = 2*N_occ(ie. N_total_bands=20). In DACAPO case, you can use sim.eband = ElectronicBands(20); In VASP case, you can set NBANDS = 20 in INCAR file.

    (b) insufficient K-point sampling in your DFT calculation
    Just like atomic or molecular orbitals, QUAMBOs are localized around ions in real-space and it may has a range of several Angstroms. That means when you calculate periodic systems(ie. crystal or surface), you need to include enough large periodic space in the Born von-Karman(BvK) boundary condition, otherwise QUAMBO would overlap with itself in other image cells. And BvK is normally realized by K-point sampling in DFT codes. You need to increase K-point sampling by setting sim.kpt = NetCDF.Entry( name="KpointSetup", value=[9,9,9]) in DACAPO case and setting
    9 9 9
    0. 0. 0.

    in KPOINTS file in VASP case.
    NOTE that only Monkhorst-Pack K-point sampling is supported by the current QUAMBO code.

    (c) incorrect or overcomplete pseudoatomic orbital basis-set in QUAMBO construction
    During QUAMBO construction, we do not need too many atomic orbitals as basis-set since some angular momentum channels will have very small portions in the bonding and antibonding orbitals. Therefore, overcomplete basis-set may give troubles in the matrix diagonalization. You may remove these pseudoatomic orbitals in QUAMBO construction by changing the "QuambInput.m" file:
    Input.ConvertPsp.AddOrDeleteOrbital = -1; % -1: delete orbital, 0: do nothing, 1 for add orbital
    Input.ConvertPsp.DeleteOrbitalType = [1]; % pseudopotential index
    Input.ConvertPsp.DeleteOrbitalIndex = [2]; % pseudoatomic orbital index for the above pseudopotential index

  2. For chemical bonding analysis, what kind of basis-set shall I use?

    Actually we found that if we include additional angular momentum channels in QUAMBO construction, Mulliken charge will be different. For example, in the case of Pt(111) surface with Oxygen atom absorbed, we should use atomic orbitals sd for Pt and sp for O. If we use dsp for Pt and sp for O, Mulliken charge is different from the previous case. The reason is that the additional p orbitals share the same character as neighbors' orbitals. We need to use the minimal basis-set instead of using overcomplete basis-set.

  3. Can I do K-point sampling in DFT calculation with symmetry?

    Yes, you can run your DFT calculation with symmetry included. In our QUAMBO code, We transform Bloch wavefunctions for each irreducible K-point to those Bloch wavefunctions for the corresponding reducible K-point in the first Brillouin zone. That means you can save a lot of time in DFT calculation by using the crystall or surface symmetry.

  4. Can I do band structure calculation by my own K-point path during the post-processing of QUAMBO?

    Yes, you can. You only need to specify three entries in "QuamboInput.m" file.
    Input.BandStructure.CrystalStructure = ['DEF']; % use 'DEF' tag to define your own k-path
    Input.BandStructure.DefinedKPathName = ['GHNPGN']; % K-path label for each K-point [G for Gamma]
    Input.BandStructure.DefinedKPath = ...
    [ 0 0 0; ...
    -1/2 1/2 1/2; ...
    0 0 1/2; ...
    1/4 1/4 1/4; ...
    0 0 0 ; ...
    0 0 1/2;
    ]; % the corresponding K-path

    see the example at "example/DACAPO/Fe_bcc/QuamboInput.m" or "example/VASP/Fe_bcc/QuamboInput.m". We also include some pre-defined K-point paths for FCC, BCC and HCP. For example, you can use them by setting:
    Input.BandStructure.CrystalStructure = ['FCC'];

Bug report



  1. [QO method] "Quasiatomic Orbitals for ab initio tight-binding analysis"

    Xiaofeng Qian, Ju Li, Liang Qi, Cai-Zhuang Wang, Tzu-Liang Chan, Yong-Xin Yao, Kai-Ming Ho, and Sidney Yip.

    Phys. Rev. B   78,   245112  (2008) [ Online | PDF ]

  2. [QUAMBO method] T.-L. Chan, Y. X. Yao, C. Z. Wang, W. C. Lu, J. Li, X. F. Qian, S. Yip, and K. M. Ho, " Highly localized quasiatomic minimal basis orbitals for Mo from ab initio calculations ," Phys. Rev. B 76 (2007) 205119.

  3. [QUAMBO method] Wen-Cai Lu, Cai-Zhuang Wang, Klaus Ruedenberg and Kai-Ming Ho, "Transferability of the Slater-Koster tight-binding scheme from an environment-dependent minimal-basis perspective," Phys. Rev. B 72 (2005) 205123.

  4. [QUAMBO method] Wen-Cai Lu, Cai-Zhuang Wang, Michael W. Schmidt, Laimutis Bytautas, Kai-Ming Ho and Klaus Ruedenberg, "Molecule intrinsic minimal basis sets. I. Exact resolution of ab initio optimized molecular orbitals in terms of deformed atomic minimal-basis orbitals," J. Chem. Phys. 120 (2004) 2629-2637.

  5. [QUAMBO method] Wen-Cai Lu, Cai-Zhuang Wang, Michael W. Schmidt, Laimutis Bytautas, Kai-Ming Ho and Klaus Ruedenberg, "Molecule intrinsic minimal basis sets. II. Bonding analyses for Si4H6 and Si2 to Si10," J. Chem. Phys. 120 (2004) 2638-2651.

  6. [QUAMBO method] Wen-Cai Lu, Cai-Zhuang Wang, Tzu-Liang Chan, Klaus Ruedenberg and Kai-Ming Ho, "Representation of electronic structures in crystals in terms of highly localized quasiatomic minimal basis orbitals," Phys. Rev. B 70 (2004) 041101.







  Last update: 3/25/2008

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