From owner-chemistry "-at-" ccl.net Thu Feb 11 16:16:00 2021 From: "Susi Lehtola susi.lehtola\a/helsinki.fi" To: CCL Subject: CCL: Static polarizability of Atoms with Gaussian or Gamess Message-Id: <-54275-210211161402-7676-8ygtl/6z+5p/6aHM3afVfA*server.ccl.net> X-Original-From: Susi Lehtola Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset=US-ASCII Date: Thu, 11 Feb 2021 16:13:44 -0500 MIME-Version: 1.0 Sent to CCL by: Susi Lehtola [susi.lehtola^^^helsinki.fi] Dear Krishna, your basis set is simply too small: 6-311+G(2d,p) is a double-zeta basis set, which does not even include diffuse functions on hydrogen. You need to go to bigger basis sets. Repeating your calculation I get Basis Polarizability (bohr^3) 6-311+G(2d,p) 0.59 cc-pVDZ 0.63 cc-pVTZ 1.88 cc-pVQZ 2.74 cc-pV5Z 3.22 cc-pV6Z 3.57 You see that the convergence is very slow in terms of the basis set size. This is often an indicator of important functions missing from the basis set. Indeed, electrical properties like the dipole moment or polarizability are well-known to be sensitive to diffuse functions. Even augmented Pople sets, however, yield very poor results: 6-31++G** 0.25 6-311++G** 0.59 Repeating the calculations in the augmented Dunning series gives much better convergence aug-cc-pVDZ 4.29 aug-cc-pVTZ 4.48 aug-cc-pVQZ 4.50 aug-cc-pV5Z 4.49 aug-cc-pV6Z 4.49 The result is essentially converged already with the triple-zeta basis, and it is in excellent agreement with the experimental value of 4.50. -- -------------------------------------------------------- Mr. Susi Lehtola, PhD Adjunct Professor susi.lehtola]![helsinki.fi University of Helsinki http://susilehtola.github.io/ Finland -------------------------------------------------------- Susi Lehtola, FT dosentti susi.lehtola]![helsinki.fi Helsingin yliopisto http://susilehtola.github.io/ --------------------------------------------------------