# DFT calcualtion without frozen core

3 years 4 months ago #744 by houqq
Dear MRCC developers,

I want to do a DFT calculation without frozen core, but I find there is no change when I set core=0

I use below input:
# DF-RKS
basis=def2-TZVPP
dfbasis_scf=AUTO
calc=PBE
mem=500MB
agrid=LD0302
rgrid=GC
grtol=12
scftol=8
core=0 #use [i]frozen[/i] for Frozen core approximation
mult=1

unit=angs
geom=xyz
2

Br      1.292519    0.000000    0.000000
Br     -1.292519    0.000000    0.000000

According to the output, MRCC should do a Frozen core calculation in DFT if my understanding is right(Frozen 28e for Br, Frozen a big core?).

If I set core=0 in input, I still get below information in output:
Number of atoms:              2
Charge:                       0
Number of electrons:         70
Number of core electrons:    56
Spin multiplicity:            1
And I still get the completely the same output and also completely the same total energy as the default Frozen core approximation:
***FINAL KOHN-SHAM ENERGY: -5147.5193772187431023 [AU]

It seems that the option core=0 is no meaning in DFT calculation?
How can I or it is possible do a NoFrozenCore DFT calculation in MRCC?

Qinqing

3 years 4 months ago #745 by kallay
Dear Qinqing,
please note that the core keyword is only effective for correlation calculations. For DFT, all electrons are treated on an equal footing, and "frozen core" is meaningless.

Best regards,
Mihaly Kallay

3 years 4 months ago #746 by houqq
Dear Kallay,

Thanks so much for your clarification.

I hear that some code like ADF, indeed do a frozen core like DFT calculation, core orbitals from all-electron atomic calculations are used in frozen (but intact) form when calculating the atomic wavefunctions.

Qinqing

3 years 4 months ago #747
Dear Qinqing,

Based on your description It is hard to find out what do you need precisely.
You should maybe specify it more, include a reference to a publication/code manual page, etc.

In the context of our DFT program, frozen core is in effect only if you select double-hybrid DFAs, which have a correlation calculation part, as wrote by Mihály.

You might think of the different but vaguely related concept of effective core potentials (ECPs). You should look at the discussion of the ecp keyword to see if that is relevant to you.

Best regards,
Peter