3.4.2 **Basic calculations with the LCAO basis set**
In this section we will describe how to do LCAO calculations using ABACUS. Again the crystal Si in the diamond structure will be taken as an example.
For convenience, first also create a subdirectory in directory ABACUS/
**mkdir -p test/Si_diamond_lcao**
Then change to this directory, and copy the STRU file, the pseudopotential file, and in addition the numerical atomic orbital file here
**cd test/Si_diamond_lcao**
cp $ABACUS_DIR/data/structures/0 collection/Si2_diamond.stru STRU
cp $ABACUS_DIR/data/elements/14_Si/1 LDA/Si.pz-vbc.UPF ./
cp $ABACUS_DIR/data/elements/14_Si/1 LDA/Si_lda_8.0au_50Ry_2s2p1d ./
The INPUT file is similar to that in section 3.4.1, and only the values of following two parameters are different:
**basis_type** lcao
**ks_solver** hpseps
• **ks_solver** The method to solve Kohn-Sham equation. Default value is cg, thus the conjugate gradient method. Here hpseps means using a High Performance Symmetric Eigenproblem Solvers package (HPSESP) [8].
The KPT file is the same as that in section 3.1.3.
**$ABACUS_DIR/bin/ABACUS.fp mpi-v$num.x**
The information printed on the screen is different from that obtained using the plane-wave basis,
...
ITER ETOT(eV) EDIFF(eV) DRHO2 TIME(s)
HP1 -2.151753e+02 0.000000e+00 1.685e-01 1.204e+01
HP2 -2.152145e+02 -3.919739e-02 3.471e-02 1.169e+01
HP3 -2.152153e+02 -8.138606e-04 3.748e-03 1.164e+01
HP4 -2.152153e+02 -9.146924e-06 4.226e-05 1.221e+01
...
The string HPn in the first column means that the HPSEPS eigenvalue solver is used, and this is the n-th self-consistent KS iteration. In contrast, the output information from the PW calculation has the string CGn in its first column, indicating the Conjugate Gradients (CG) method is used to solve the Kohn-Sham equation.
In many cases, only one Γ point (i.e., k=0) is needed in the calculations. In these cases, one can set in the INPUT file:
• **gamma_only** If set to 1, only Γ point is used in the calculation. The gamma_only algorithm is much faster than the standard algorithm. |