CPMD

Local Modifications

Local modifications to CPMD:

• &QMC and &SYM sections to the input file.
• Calculate symmetry of the states.
• Compute integrals of the type <math><i|v_{xc}|j></math> and <math><ij|kl></math>.
• Integration with NECI code (mainly qmc* subroutines, plus antisymint.F). NECI code resides in the NECI subdirectory.

Input file options

The following are in addition to the options given in the manual for CPMD v3.11.1.

&CPMD section

• QMC

Run NECI code using Kohn-Sham orbitals generated by CPMD. Need to perform a wavefunction optimization calclulation first---requires the RESTART file and the QMC input file (default filename: inp.)

• 4-INDEX INTEGRALS

Compute the integrals <math><i|v_{xc}|j></math> and <math><ij|kl></math> if not doing a QMC run. (Calculated on the fly or as an initialisation for QMC jobs.)

• RESTART SYMMETRY 2-INDEX 4-INDEX

Read in the symmetry, <math>v_{xc}</math> and 4-index integrals respectively, from the files SYMMETRY, 2INDEXINT and 4INDEXINT.

&QMC section

Specify options relevant to a QMC job.

• INPUT FILE <filename>

QMC input filename.

• MEMORY ALLOCATE <Memory in MB>

Specify the size of memory block to use to store wavefunctions in real space in MB. Default is 500MB.

• INTEGRALS FAST

Compute the four-index integrals quicker using a coarser mesh (currently not working---don't use).

• INTEGRALS PRINT

Print out the 'non-special' <math><ab|cd></math> integrals to the file abcdint.

&SYM section

Options for symmetry code.

• CALC SYM [ALL,OFF]

ALL: Calculate characters due to rotational symmetry for all operations rather than by classes (default). If the system is non-symmorphic, then characters are found for each operation automatically.

OFF: Turns symmetry off (by setting each state to be totally symmetric).

• INTERPOLATE <NSHELLS>

A symmetry operation may not necessarily move us from one mesh point to another. A Lagrange interpolation process is used to find the wavefunction by using NSHELLS (default 1) of boxes around the point (i.e. an interpolation of order 2*NSHELLS-1). The scaling is not so nice, but you shouldn't really need to ever go above 2 (and 1 is almost always good enough).

• INT STEP <SYMINTSTEP>

The calculation of characters by <psi|R|psi> over the real space mesh is fairly costly. Integrating using a step size of SYMINTSTEP (default 1) can speed things up significantly for large high-symmetry systems. Integrating using every other point (INT STEP 2) is a good value---there appears to be little loss in accuracy. SYMINTSTEP=4 is less good (i.e. really shouldn't be used). A check is made the the specified value is consumerate with the real space mesh (if it isn't, then SYMINTSTEP=1 is set).

• TRANS SYM OFF

Turn off translational symmetry for supercells. (Not applicable if space group symmetry is used.)

• SPACE GROUP [OFF]

Use rotational and translational symmetry (if applicable) separately, rather than all the symmetry operations of the space group.

• DEGEN TOL <DEGEN TOL>

Specify the tolerance for two states to be considered degenerate. Default is 1.d-6.

&QMC section

Specify options relevant to a QMC job.

• INPUT FILE <filename>

QMC input filename.

• MEMORY ALLOCATE <Memory in MB>

Specify the size of memory block to use to store wavefunctions in real space in MB. Default is 500MB.

• INTEGRALS FAST

Compute the four-index integrals quicker using a coarser mesh (currently not working---don't use).

• INTEGRALS PRINT

Print out the non-special <math><ab|cd></math> integrals to the file abcdint.

&SYM section: Options for symmetry code.

• CALC SYM [ALL,OFF]

ALL: Calculate characters due to rotational symmetry for all operations rather than by classes (default). If the system is non-symmorphic, then characters are found for each operation automatically.

OFF: Turns symmetry off (by setting each state to be totally symmetric).