From owner-chemistry@ccl.net Wed Jul 27 12:26:01 2022 From: "Andrew DeYoung andrewdaviddeyoung*o*gmail.com" To: CCL Subject: CCL:G: Comparing the computational cost of BLYP and B3LYP Message-Id: <-54776-220727122410-27687-IH+vapOhCu6OTPSzpaz0Xg^server.ccl.net> X-Original-From: Andrew DeYoung Content-Type: multipart/alternative; boundary="00000000000044c76b05e4cbd804" Date: Wed, 27 Jul 2022 12:23:51 -0400 MIME-Version: 1.0 Sent to CCL by: Andrew DeYoung [andrewdaviddeyoung(a)gmail.com] --00000000000044c76b05e4cbd804 Content-Type: text/plain; charset="UTF-8" Hi, I am rather new to quantum chemical calculations, and I am wondering if you can help me make sense of some benchmark timing results I obtained from Gaussian 16. I ran Gaussian 16 calculations of an ion pair with a total of 31 atoms (18 atom cation, 13 atom anion). I obtained the following wall-clock timings for various combinations of method and basis set: HF/6-31G, 6.47 sec HF/6-31G(d), 14.21 sec HF/6-31G(d,p), 18.93 sec BLYP/6-31G, 20.35 sec BLYP/6-31G(d), 46.43 sec BLYP/6-31G(d,p), 56.93 sec BLYP+D3/6-31G(d,p), 57.68 sec B3LYP/6-31G, 18.21 sec B3LYP/6-31G(d), 32.50 sec B3LYP/6-31G(d,p), 41.17 sec B3LYP+D3/6-31G(d,p), 41.24 sec I am not surprised that HF is the least computationally expensive method of the three, but I am surprised that, according to these results, BLYP is more expensive than B3LYP. Should I be surprised by this? I was under the impression that BLYP is rather popular in ab initio MD precisely because it is less expensive than B3LYP. (Of course, Gaussian does not, as far as I know, do ab initio MD, so perhaps BLYP's greater expense in Gaussian is just due to implementation; I'm guessing BLYP is not that popular for electronic structure these days, so perhaps its implementation in Gaussian is not as optimized as the immensely popular B3LYP?) B3LYP is a hybrid functional, while BLYP is not, but I realize that this does not, by itself, mean that BLYP should be less expensive than B3LYP. Thanks, Andrew Andrew DeYoung, PhD Department of Chemistry Carnegie Mellon University --00000000000044c76b05e4cbd804 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
Hi,

I am rather new to quant= um chemical=20 calculations, and I am wondering if you can help me make sense of some=20 benchmark timing results I obtained from Gaussian 16.

I ran Gaussian 16 calculations of an ion pair with a total of 31 atoms=20 (18 atom cation, 13 atom anion).=C2=A0 I obtained the following wall-clock= =20 timings for various combinations of method and basis set:

HF/6-31G, 6.47 sec
HF/6-31G(d), 14.21 sec
HF/6-31G(d,p), 18.93 sec

BLYP/6-31G, 20.35 sec
BLYP/6-31G(d), 46.43 sec
BLYP/6-31G(d,p), 56.93 sec
BLYP+D3/6-31G(d,p), 57.68 sec=20

B3LYP/6-31G, 18.21 sec
B3LYP/6-31G(d), 32.50 sec
B3LYP/6-31G(d,p), 41.17 sec
B3LYP+D3/6-31G(d,p), 41.24 sec

I am not=20 surprised that HF is the least computationally expensive method of the=20 three, but I am surprised that, according to these results, BLYP is more expensive than B3LYP.=C2=A0 Should I be surprised by this?=C2=A0=C2=A0

I was under the impression that BLYP is rather popula= r in ab initio MD precisely because it is less expensive than B3LYP.=C2=A0 = (Of course, Gaussian does not, as far as I know, do ab initio MD, so perhap= s BLYP's=C2=A0greater expense in Gaussian is just due to implementation= ; I'm guessing BLYP is not that popular for electronic structure these = days, so perhaps its implementation in Gaussian is not as optimized as the = immensely popular B3LYP?)

B3LYP is a hybrid functional, while BLYP is not, but I realize that this does no= t, by=20 itself, mean that BLYP should be less expensive than B3LYP.
<= br>
Thanks,
Andrew

Andrew DeYoung, PhD
Department of Chemistry
Carneg= ie Mellon University
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