I highly recommend purchasing NEC-5 and using it with EZNEC Pro+, even if you have EZNEC Pro/4+. Some of its many advantages are described below and in the EZNEC Pro+ manual Calculating Engines topic. And the current price for individual use is less than even EZNEC+ was -- just $110.
See LLNL for links to ordering and current pricing.
Features
Allows buried conductors
Not subject to stepped diameter errors
Insensitive to insertion object placement
Not subject to several other NEC-2 and NEC-4.2 sensitivities and restrictions
External NEC-5 program (purchased from LLNL) can be used with EZNEC Pro/2+ and EZNEC Pro/4+
External NEC-5 program is relatively inexpensive and fast
NEC-5 was first released in early 2020. Its principal author, Gerald "Jerry" Burke regrettably passed away just one year later. NEC-5 is a remarkable work and a worthy legacy but the inevitable few bugs, some unfortunately serious, have been discovered in the program. As of this writing in May 2022, LLNL hasn't found anyone to support NEC-5 and be committed to correcting these or make future changes as necessary.
So that EZNEC Pro+ users can have a more bug-free NEC-5 to use, and with the very extensive help of Dan Maguire AC6LA (author of AutoEZ) in finding, testing, and verifying, I fixed the bugs we've found and recompiled the NEC-5 console program which EZNEC Pro+ can use for calculations. LLNL has agreed to distribute this with new NEC-5 purchases and provide no cost updates to users who purchased the original program. See LLNL for purchasing and update information. Note that only the "command line" or "console" program originally named NEC5CL.exe has been modified; the bugs remain in the other program types currently being distributed by LLNL.
The initial debugged NEC-5 program was called NEC-5 x11. Additional bugs were found and a second debugged version was developed and released on May 13, 2022. The current debugged program is called NEC5 x13.
In the EZNEC Pro+ Utilities menu is a selection that lets you easily tell if the NEC-5 program you're using is a modified one. The original, unmodified program can give incorrect results when using current sources or MININEC type ground, and crash under some circumstances. The causes of those are fixed in the x11 version, but other potentially serious errors existed under some conditions when using Real, Extended Accuracy ground which weren't known at the time of that modification. Those have been fixed in the current x13 version. The current modified console program is identified as "x13" on the second line of its output file. Note that, like x11, the x13 modification has been done only to the "command line" or "console" program originally named NEC5CL.exe.
For additional information about updating older versions to x13 and much more information about the bugs found and fixed v. x13, see 'NEC-5 engine second revision now available' by AC6LA.